
EOGRAPH\ 



R. E 




pBABLJJ 






"i^te'vi 


jUmg 


**■*>*- S 


"I-— - j' ; ^4 






Jf^^^ 


■■ibh 

■ | 




' . .«Mt 


BB 














mWUM 



LIBRARY OF CONGRESS. 



Chap. Copyright No.. 

Shelf.rR-3-£- 



UNITED STATES OF AMERICA. 



Digitized by the Internet Archive 
in 2011 with funding from 
The Library of Congress 



http://www.archive.org/details/elementaryphysic02redw 



ELEMENTARY 
PHYSICAL GEOGRAPHY 



elementary 
Physical Geography 

AN OUTLINE OF PHYSIOGRAPHY 



BY 

JACQUES W. REDWAY 



Vie waste of the Old Land is the material of the New 



NEW YORK 

CHARLES SCRIBNER'S SONS 

1900 



12392 

Library of Congress 

Two Copies Received 
JUN 29 1900 

Copyright entry 
Ho.A. ../Sf.l/.. 

SECOND COPY. 

Delivered to 

ORDER DIVISION, 
AlIP, 3 1900 



Copyright, 1900 by 
JACQUES W. EEDWAY 



7-cSO. 



TROW DIRECTORY 
PRINTING AND BOOKBINDING COMPANY 



PREFACE 

The science of Geography sets forth the relations of life 
and its environment to the earth, and it is the function of 
both the writer and the teacher of geography to explain 
these relations. In the Elementary Natural Geography 
the pupil studies the various peoples of the earth and the 
countries in which they live ; in the Advanced Geogra- 
phy there is presented in addition a discussion of the 
industries of life and their geographic distribution. In the 
present volume, which the author has prepared as a log- 
ical sequel, it is designed to show that the distribution of 
life is governed very largely by the conditions of geo- 
graphic environment, and that human history and indus- 
tries are always closely connected with geographic laws 
— in many instances the direct- resultants of them. 

The science of Geography as now understood includes 
something more than a mere description of topographic 
forms — it comprehends the gradual and progressive devel- 
opment of these forms and their results as regards life, as 
well. It includes also the effects of temperature and 
moisture, for life and its activities depend also on them. 
That is, it naturally involves the principles of Descriptive 
Geography, Physiography, and Economics; and the pres- 
ent volume is designed to show their interrelation. 

In scope this book contains all the principles recom- 
mended by the Committee; of Fifteen, and such other feat- 
ures as have suggested themselves to the author. It is 
designed to be used in the junior grades of the High 



vi PEEFACE 

School, and in Normal Schools. With judgment in the se- 
lection of the topics, it may be begun in the last half of 
the eighth year of the Grammar School. The arrange- 
ment of the subjects is logical, but the teacher may readily 
organize a course of study in the subject without reference 
to the present arrangement. To make this more easily 
accomplished, the principles of the subject are set forth in 
the larger type ; relevant matter that is illustrative but 
non-essential is confined to the notes. In general, the 
teacher should not hesitate to omit a topic the discussion 
of which is too difficult for the class. 

The Questions and Exercises are designed to stimulate 
observation and independent thought. If, occasionally, 
they leave the pupil in doubt, the design of the author will 
be fulfilled. The pupil must learn by experience that 
knowledge does not come in cut-and-dried packages ; it 
comes only after long and painstaking investigation. 

In the preparation of the work the author takes pleasure 
in acknowledging the material assistance of Miss Frances 
Bronson, and of his daughter, Miss Elizabeth Ebert Red- 
way. But to more than anyone else, however, thanks are 
due to Miss Stella Wilson, Instructor in Physical Geog- 
raphy in the Central High School, Columbus, Ohio. To 
Miss Wilson's keen judgment, excellent criticism, and ex- 
perience are largely due the usefulness as a text-book which 
this volume may have. 

The books designated for reference and collateral read- 
ing are intentionally few in number, and those most com- 
monly cited should be in the school library. The teacher 
will also find it very advisable to get in close touch with 
the United States Geological Survey and the Weather 
Bureau. The Bureau of Geography recently established 
at Winona, Minn., will also be helpful. 

J. W. R. 



CONTENTS 



PAGE 

Introductory, . . . 1 

CHAPTER 

I. The Earth Among Planets ...... 9 

II. The Structure of the Earth 20 

III. Land and Water, and their Outlines . . .41 

IV. The Eesults of Slow Movements of the Rock 

Envelope : Plains, Plateaus, and Mountains . . 56 

V. Destructive Movements of the Rock Envelope : Vol- 
canoes AND THEIR PHENOMENA ..... 80 

VI. Destructive Movements of the Rock Envelope : 

Earthquakes 95 

VII. The Wasting of the Land : The Work of Rivers . 105 

VIII. The Wasting of the Land : The Work of Under- 
ground Waters 132 

IX. The Wasting of the Land : The Work of Ava- 
lanches and Glaciers 150 

X. The Wasting of the Land: The Results of Im- 
perfect Drainage and Obstructed Lakes and 
Marshes 165 

XI. Ocean Waters and their Movements : Waves, Tides, 

and Currents . . . . • • • .190 

XII. The Atmosphere and its Properties : Winds . .214 

XIII. The Moisture of the Atmosphere : Seasonal and 

Periodical Distribution of Rainfall . . . 231 



viii CONTENTS 

CHAPTER PAGE 

XIV. The Moistube of the Atmosphere : Cyclonic Storms 248 

XV. Electrical and Luminous Phenomena of the Atmos- 
phere 268 

XVI. Climate and its Factors 287 

XVII. The Dispersal of Life 303 

XVIII. Geographic Distribution of Plants and Animals . 315 

XIX. Man 335 

XX. The Industrial Eegions of the United States . 352 

Appendix 375 

Index 381 



PHYSICAL GEOGRAPHY 



INTEODUCTOEY 

Only a casual thought is needed to make it apparent 
that life on the earth, as we now find it, depends on a very 
delicate adjustment to its surroundings. Living beings 
require certain conditions of heat, moisture, and geo- 
graphic environment; and if these are changed ever so 
slightly the life forms must adjust themselves to the new 
conditions, or else they must seek a new abiding-place ; 
or, perhaps, they may perish altogether. 

For instance, turf grass requires water at very short 
intervals, and if for several successive years there are 
droughts of five or six months' duration, it will die. And 
if there are herds of cattle in the region, they must adjust 
themselves to the changed conditions. They must adapt 
themselves to other food, or they must migrate. Other- 
wise they too will perish. 

Were the temperature of the earth to change only a few 
degrees there would be a similar disturbance that would 
involve almost every living thing. And if it should fall so 
low that the water were everywhere frozen, life as we now 
know it could not exist any great length of time, because 
living beings need in their structure a large proportion of 
water, and the latter must be taken into the structure in 
a liquid form. For a similar reason, if all the water were 
in the form of vapor, life could not long endure unless the 

1 



2 PHYSICAL GEOGKAPHY 

life forms were very different in structure from those with 
which we are acquainted. 

Life is by no means evenly distributed over the earth, 
however. A few species spend the greater part of their 
existence in the air, and a larger number live in water only. 
By far the greater number of species, however, live at the 
plane of contact between the atmosphere and the earth's 









?#» 




m 



A FERTILE VALLEY, NEW YORK 

Capable of producing abundant food-stuff's, and densely peopled. 

rock envelope — that is, on the land surface of the earth. 
Their distribution is governed by the conditions of warmth, 
moisture, and surface, and if these conditions were to 
change ever so slightly, the distribution would be disturbed. 
Life and its distribution are governed by geographic laws ; 
if the latter change, no must the former. 

Man, who stands at the head of animate nature, is able 
to endure a much wider range of warmth, moisture, and 



INTRODUCTORY 3 

surface features than most other living beings. He can 
withstand extremes of heat and cold that are fatal to most 
other animals, and he can live indifferently in places of 
great drought or of excessive moisture. The arctic re- 
gions are not so cold, nor the tropical lands so hot that 
man cannot dwell there ; and throughout the wide world 
one can find scarcely an ice-clad summit or a sun-beaten 
desert in which human beings have not lived. 

On account of these varying conditions — all the result of 
geographic laws — the study of the earth is both important 
and interesting, because it is the home of man. Like all 
forms of life, man requires food ; more than any other ani- 
mal, he needs shelter. His food, of which he consumes 
about eighty tons during the three or four score years of 
his existence, comes from the earth — the land, the water, 
and the air each yielding part — and the materials that are 
used for clothing and shelter come also from the same 
source — the earth. 

So, in order to understand the story of life, its history 
and its industries, one must learn about the pl^sical geog- 
raphy of its surroundings — that is, about its environment, 
or the various conditions of heat, moisture, and surface 
features. Land animals could not live until the waters 
were separated from the land. Before they could main- 
tain life, vegetation must have spread itself over the land ; 
and before vegetation could endure there must have been 
soil. And before there could be soil, the surface of the 
land must have been folded, broken, worn, and furrowed, 
so that the fragments of rock could be ground fine and 
formed into soil. All these earth-weathering processes 
must have been going on before the higher forms of life 
could exist, and all over the surface of the land such 
changes are even now going on from day to day. Scarcely 
a summer shower falls that does not leave its marks ; and, 



4 



PHYSICAL GEOGRAPHY 



indeed, throughout the physical history of the earth the 
most apparent feature is constant change. 

From the time the land was first divided from the waters, 
the continents, or great bodies of land have been ever 
changing. In places, alternately sinking, rising, and 
warping in various ways, the shore outlines have taken 
various forms. Rugged coasts sinking below sea-level 
have resulted in the fjorded shores, such as those of the 




ARCTIC LANDS 
Too cold and not enough soil for the support of life. 

North Atlantic States, making the harbors where so much 
of the manufacture and commerce of the country have 
centred. Rising coasts have lifted natural harbors above 
sea-level, making the approaches to the land so difficult 
that vessels can find no sheltered anchorage. Old sea- 
bottoms, covered with sediments that form the richest 
soil, have been lifted above the sea, and in time have be- 
come densely peopled areas. 



INTRODUCTORY 5 

Certain forces are causing tlie surface of the rock en- 
velope to wrinkle and fold, forming plateaus, mountains, 
and valleys ; and at the same time the waters of the atmos- 
phere, falling as rain or snow, are constantly at work wear- 
ing awaj T the wrinkles and folds, carrying the material back 
to the sea. 

It is necessary to know about these processes, and to 
understand how they are going on, because almost every 
form of life is more or less modified by them, and certainly 
the history and the industries of man are very largely gov- 
erned by them. Man may rise superior to his environ- 
ment — that is, his geographic surroundings — but he is al- 
ways more or less modified by it. Mountains and valleys, 
plains and plateaus, oceans and rivers, have all been potent 
factors in making the destiny of peoples. 

The rugged and barren slope of Norway forbade an}' 
great development of agriculture, while the deeply fjorded 
shores invited the pursuits of the sea. The Norse people, 
therefore, became sea rovers and magnificent sailors. The 
uncultivable mountains of Greece could not well yield the 
food-stuffs necessary for the population, so we find a his- 
tory of " Greece scattered." From the remotest times the 
rich valley of the Tigris and Euphrates, because of its fer- 
tility, has always attracted people, and we therefore find it 
a densely settled region. 

Unless there is something to unfit them for human habi- 
tation, lowlands are favorite places of dwelling, and by far 
the greater part of the world's population is found in them. 
How is the statement borne out in the case of the Central 
Plain of North America? — the swampy, forest plain of 
the Amazon ? — the great lowland region of southeastern 
Asia? — the northern plains of Eurasia? 

Kiver bottom-lands, also, are nearly always densely peo- 
pled. How is this illustrated in the history of Egypt?— 



6 PHYSICAL GEOGRAPHY 

with regard to the nations dwelling in the Mesopotamia ? 
— the valley of the Ganges? — the bottom-lands of the 
Mississippi River ? — the Sacramento-San Joaquin Valley ? 
Extensive desert regions are always sparsely peopled ; 




A RUGGED NORWEGIAN SLOPE 
A locality not suitable for farming ; a few food-plants may be grown. 

why? How is this illustrated in the eastern and west- 
ern halves of the United States ? The population of 
rugged highlands and mountain ranges is usually sparse ; 
is there a good reason therefor ? 

The hot regions of the land are almost always densely 
peopled, the deserts and forest swamps excepted. Is this 



INTRODUCTORY 7 

true of the intensely cold regions ? Life thrives best in 
regions of warmth and of strong sunlight. Are all parts 
of the earth equally warmed ? Have all parts the same in- 
tensity of light? Compare the density of population of 




A TROPICAL SCENE 
Both temperature and moisture are favorable to a great productivity of food-stuffs. 

cold and dimly lighted parts of the earth with that of the 
warm and strongly lighted parts : in which is it greatest ? 

The study of the distribution of heat and cold, of rain 
and drought, of highlands and lowlands, and of fertile and 
unfertile regions form an essential part of the study of 
geography ; the study of the progressive changes that have 
been and are now taking place on the earth's surface con- 
stitutes the science of physiography, or "nature-writing." 



8 PHYSICAL GEOGKAPHY 

The object of this book is to show that the fundamental 
laws of geographic science not only control the structure 
of life forms and their distribution over the earth, but that 
they also largely control and modify the history, the activi- 
ties, and the various economies of man, as well. 

QUESTIONS AND EXERCISES.— What are the leading industries 
of the city or town in which you live ? Note and describe a geographic 
feature that favors any one of these industries, and without which the 
industry could not thrive. 

What would be the effect, so far as the habitability of the sur- 
rounding region is concerned, were the rainfall to be diminished one- 
half ? 

How would a material change in the surface features affect the indus- 
tries ? 

On p. is a map of New York Harbor ; what would be the effect on 
the commerce of the port if the surface of the water were lowered two 
hundred feet ? 

Mention two or more reasons why lowland regions are more densely 
peopled than highlands. 

Quito, the capital of Ecuador, is in the midst of a fertile region nearly 
two miles above sea-level ; what are its advantages over the coast plain 
region to the westward ? 

Make a list of half-a-dozen or more extensive regions that are not 
habitable, and explain the geographic reasons for their condition. 



COLLATERAL READING. 

Mill. — Realm of Nature, pp. 331-336. 
Shaler. — Nature and Man in North America. 



CHAPTEE I 
THE EAETH AMONG PLANETS 

The Solar System. — The cluster of heavenly bodies 
called the solar system is one of a great number of groups 
in space. The members of this group revolve about a 
common centre of gravity, however, and for this reason 
they are called collectively a system. The number of 
bodies composing it is unknown. 

The members of this system vary greatly in size. The 
largest is about 886,000 miles in diameter, and the small- 
est are probably too minute to be measured by ordinary 
standards. Eight of them, however, are three thousand 
miles, more or less, in diameter, and a large number, about 
four hundred, vary from ten miles to less than live hundred 
in diameter. 

The largest member of the solar system, the sun, is 
about eight hundred times as large as all the others to- 
gether, and the common centre of gravity around which 
they revolve is very near to it or, perhaps, within its mass. 
The eight bodies next in size are called /Janets, and all but 
two of them are attended each by one or more satellites or 
moons. The four hundred or more small planets are called 
asteroids, 1 or, more properly, planetoids. In addition 
there are several counts- and groups of meteors 3 that 
have a permanent place in the solar system. 

There is much evidence to show that the planets are 
composed of the same kinds of substance or material, but 
it seems certain that they are very unlike one another in 

1) 



10 



PHYSICAL GEOGRAPHY 



physical condition ; for while some, bulk for bulk, are but 
little heavier than water, others are about as heavy as iron 
ore. It seems certain also that this difference is largely a 
result of temperature ; for while some of the planets have 




Neptune 



THE SOLAR SYSTEM 
The space within the orbit of Jupiter shows the relative si^e of the Sun. 

apparently lost the greater part of their heat, others still 
are very hot. The sun, for instance, is a glowing mass 
surrounded by white-hot vapors, and its heat is probably 
greater than any artificial heat known. 



THE EARTH AMONG PLANETS 



11 



The Sun and the Planets. — The similarity of the sun 
and the planets to one another is far more marked than 
their points of difference. All whirl around a common 
centre of gravity in a direction from west to east, and each 
turns or spins on its axis in the same direction. Each is 
nearly spherical in shape, differing from a sphere by a 




THE MOON 

From a photograph. 

curvature that in nearly every instance is a slight flatten- 
ing at the poles of their axes. Several arc known to be 
surrounded each with an atmosphere, and there is some 
evidence that this is true of all. 

It is now generally believed that the members of the 
solar system formerly existed as a body of gaseous matter ;' 
because the force of gravity drew the particles together, 



12 PHYSICAL GEOGRAPHY 

toward the centre of gravity, a rotation of the mass around 
the centre of gravity resulted. Finally, parts of the mass 
were thrown off, one after another, forming the planets. 
In the same manner, the rapid rotation of each planet 
threw off portions of its mass forming the satellites. 

Although the assumed formation of the solar system by 
this process is a matter of theory, it is a theory supported 
by evidence. The telescope reveals many such masses of 
gaseous matter showing planetary formation. The spec- 
troscope, an instrument for analyzing light, shows, not 
only the matter of which they are composed, but also that 
the matter is in rapid motion. It shows also that the 
earth and the sun contain the same kinds of matter. Cal- 
cium, hydrogen, iron, and sodium, the substances of greatest 
abundance at the surface of the sun, are also among the 
most abundant substances in the composition of the earth. 

The Form of the Earth. — The earth is one of the 
planets. From Table I: {Appendix), find how it ranks 
among the other planets in size ; — in distance from the sua. 
In form the earth resembles the other planets, being nearly 
spherical, but slightly flattened at the poles. It is usually 
said to be an oblate spheroid — that is, a sphere flattened 
at its polar diameter, but it deviates slightly from this 
form ; hence the term geoid is sometimes used to apply to 
its irregular shape. 

The spherical form of the earth is shown in various 
ways that are well known, but it is demonstrated most 
clearly by surveying a horizontal straight line along a level 
surface, such as that of a pond. 5 The line thus projected 
does not lie parallel to the surface ; the latter recedes or 
curves away from it, and the curvature is such as corre- 
sponds to the surface of a spherical body. 

Were the earth a true sphere, the weight of a body 
would be the same at every part of its surface. There is 



THE EARTH AMONG PLANETS 13 

a measurable difference, however, and it is found that a 
given body weighs a little more in polar than in equatorial 
latitudes, and from the careful experiments based on this 
fact the amount of flattening at the poles has been deter- 
mined. 

The following are its dimensions : 

Polar diameter 7,901.5 miles 

Equatorial diameter 7,926.6 miles 

Circumference at equator 24,912 2 miles 

Surface (approximate) 197,000,000 square miles 

What is the difference between the polar and the equa- 
torial diameter ? On a globe one foot in diameter the dif- 
ference would be what part of one inch ? Compare the 
diameter of the earth with that of the sun (Table I., Ap- 
pendix). Large as the earth seems to us, it would require 
about one and a quarter million bodies of its size to 
make a globe as large as the sun. 

Motions. — The earth has several distinct motions. It 
revolves about the common centre of gravity in an ellipti- 
cal path, making a complete journey in very nearly 365J 
days — a period of time called a year. It also rotates, or 
spins on its axis. The time required to make a complete 
rotation is called a day and is commonly used as a unit for 
the measurement of short intervals of time. The poles of the 
earth also move or oscillate in a nearly circular path. The 
motion resembles that of the poles of a " sleeping" top. 

The first motion combined with the inclination of the 
axis gives rise to the successive change of the seasons and 
the varying length of sunshine and darkness. The second 
motion causes the succession of day and night ; it is "day" 
in all parts of the surface turned toward the sun and 
"night " on the opposite side. The third motion causes the 
phenomenon or movement commonly known as the pre- 



14 



PHYSICAL GEOGEAPHY 



cession of the equinoxes. In long intervals of time it is 
thought that this motion is connected with certain changes 
of climate. It is a subject, however, that belongs to the 
science of astronomy, and not to physical geography. 

Effects of the Inclination of the Axis. — The axis of 
the earth is not perpendicular to the earth's path (called 
the plane of the ecliptic), but inclines about 23^ degrees, as 
shown in the accompanying figure. In long intervals of 
time the amount of inclination varies. Practically, how- 
ever, the axis points always in the same direction and 
therefore is said to be parallel to itself. The northern end 
of the axis prolonged would extend nearly in the direction 
of a star named Polaris ; this star is therefore often called 
the north star. 

If the earth's axis were perpendicular to the plane of its 
orbit, each place would have the same unvarying season. 



June 21-23/ 





INCLINATION OF THE EARTH'S AXIS 

The unshaded hemisphere shows the position of the light circle at each of the four seasons. 



It would be hot in equatorial regions, mild in mid-lati- 
tudes, and cold in polar regions, the intensity of heat in- 
creasing from the poles toward the equator. 



THE EARTH AMONG PLANETS 15 

With the axis inclined, however, the case is different. 
An inspection of the accompanying diagram shows that 
during the month of June the sun's rays fall almost verti- 
cally on mid-latitude parts of the Northern Hemisphere, 
while in the corresponding latitudes of the Southern 
Hemisphere the rays are very oblique. At this season, 
therefore the Northern Hemisphere receives more light 
and more heat than the Southern. 

Six months later the conditions are reversed; the belt 
of vertical and nearly vertical rays is in the Southern Hem- 
isphere, while in the Northern, the rays of light and heat 
are very oblique. At this season, therefore, the Southern 
Hemisphere receives its greatest warmth. Thus, it is seen, 
the amount of light and warmth received by each hemi- 
sphere varies. In equatorial latitudes the difference is not 
great, but beyond the tropics, in higher latitudes, it is the 
difference between winter and summer. In polar latitudes 
the sun is shining the greater part of the time for six 
months alternately in each hemisphere, the other hemi- 
sphere being in darkness. As a result the season of sun- 
shine, or summer, becomes oppressively hot at times, while 
the season of darkness, or winter, is intensely cold. 

The rotation or spinning of the earth on its axis causes 
the succession of day-light and darkness, or, popularly, 
" day " and " night." One-half the surface, being always 
toward the sun, is therefore illuminated, while the opposite 
side is in darkness. The rotation of the earth, however, 
presents every part successively toward the sun, lighting 
all parts in turn. Were the axis of the earth perpendicu- 
lar to the direction of the light-rays, day and night would 
be of equal duration in all parts of the earth's surface ; but 
on account of its inclination, the relative length varies, not 
only in different latitudes", but with the changes of the 
seasons in the same latitude. 



16 



PHYSICAL GEOGRAPHY 



In the torrid zone the period of daylight and darkness 
does not vary much from twelve hours each, and at the 
equator each is twelve hours long through the year. In the 
temperate zones the days are longest near the polar circles 
and shortest near the tropics, varying from thirteen to 
twenty-four hours. Within the frigid zone day and night 
correspond practically to summer and winter. There, both 
the day and the night vary from a few brief moments 

to six months in length. 
The relative length of 
daylight and darkness and 
the changes of the sea- 
sons have much to do with 
the subject of physiogra- 
phy. For their vitality 
almost all the forms of 
life depend not only on 
the presence of sunlight, 
but on the time and man- 
ner of distribution as well. 
Only a very few species 
of animals and plants 
thrive in regions of long- 
continued darkness, and 
they are mainly the lower 
forms ; the higher species require an environment in which 
light and darkness follow one after the other in periods of 
short duration. With few exceptions, plants fail to mature 
and fructify unless exposed to strong light, and many spe- 
cies will not live at all. Plants that are forced into blos- 
som in darkened rooms have usually pale or white flowers, 
and the leaves of growing plants are apt to be yellow 
instead of green. 




RELATIVE LENGTH OF DAY AND NIGHT 

The shaded part of each parallel shows the length 
of the night; the unshaded part, the proportion- 
ate length of the day. 



THE EARTH AMONG PLANETS i; 

QUESTIONS AND EXERCISES.— Make a circle one inch in diam- 
eter on the blackboard, and from the centre of this circle, with a ra- 
dius fifty-five inches long, draw as much of the arc of a circle as the 
size of the blackboard will permit. The two circles represent the 
relative size of the earth and the sun. 

In the diagram, p. 14, the axis of the earth is inclined 23! degrees 
from the dotted line ; which of these positions represents summer 
in the Northern Hemisphere ? — In the Southern ? Copy the diagram, 
p. 16, and mark the point the sun's rays reach beyond the north 
pole ; how many degrees from the pole to this point ? What circle 
passes through this point ? Mark the point on the circumference 
where the rays are vertical. What circle passes through this point ? 
From each pole to the equator the angular distance is ninety degrees : 
find the distance in degrees from the Arctic Circle to the Tropic of 
Cancer ; this distance is the width of the Temperate Zone. If the in- 
clination of axis were 28 degrees, what would be the width of each 
light-zone ? If 32 degrees ? Ninety degrees less twice the angle of in- 
clination equals the width of the Temperate Zone. 

In the diagram, p. 16, the proportionate length of the longest day and 
shortest night are shown by the shading : determine by measurement 
the length of the longest day in latitude 40° ; in latitude 60 . Sub- 
divide the parallel into tvjenty-four parts by halving it three times and 
dividing the last subdivisions each into three parts ; each of the smallest 
subdivisions has practically an hour value. 

COLLATERAL READING AND REFERENCE. 

Mill. — Realm of Nature, pp. 63-81. 

Redway. — Manual of Geography, pp. 04-78. 

Howe. — Elements of Astronomy. Problems, a-g, p. 83. 

Jacksox. — Astronomical Geography. 

NOTES 

1 The asteroids move in orbits in the space between Mars and 
Jupiter. Many of them do not exceed twenty or thirty miles in 
diameter, and the largest probably does not exceed five hundred 
miles. Their combined volume is less than one four-thousandth 
part of the mass of the earth. Eros, one of the recently discov- 
ered asteroids, has an orbit so eccentric that it crosses that of 
Mars, and at times is nearer to the earth than is Mars. 



18 PHYSICAL GEOGRAPHY 

2 But little is known about the nature and structure of 
comets, but it is thought that the chief part of their masses, in 
most instances, is gaseous matter. One comet, Temper s, un- 
doubtedly consists of a vast swarm of meteors, but it is probable 
that the various comets are differently constituted. Several of 
them belong to the solar system, but many are temporary visitors, 
coming from unknown regions of space, whirling around the sun 
and again vanishing. 

3 Meteors, or shooting stars, are small bodies that seem to ex- 
ist very generally throughout space. In a few instances they are 
seen in clusters, as in the case of Temper s comet. The earth, 
and probably the other planets, encounter many thousands of 
them daily, in sweeping through space. By far the greater num- 
ber on reaching the earth's atmosphere are heated to whiteness — 
partly by compression of the atmosphere in front of it, and 
partly by friction against it — and are dissipated as white-hot 
vapor. Some of the larger ones reach the earth, and many of 
these have been analyzed. Some consist mainly of iron and 
nickel in a metallic form ; others are composed of matter not 
differing materially from lavas. No element has yet been found 
in a meteor that does not occur in the earth, but in a few in- 
stances chemical compounds, of iron, nickel, and phosphorus, 
and certain crystalline forms, have been found in meteors that 
have never been met with naturally in terrestrial substances. In 
one instance gold, in another diamonds, wei-e found in a mete- 
orite. 

4 So far as is known, matter exists in three physical forms — 
solid, liquid, and gaseous — and nearly every chemical element 
and many of their compounds may assume each form. In the 
solid form the molecules are bound by a strong cohesion ; in the 
liquid form they are very slightly cohesive ; in the gaseous form 
they strongly repel one another. Most of the substances that in 
the earth are solids, in the sun exist as white-hot vapors. 

5 An interesting experiment is suggested by Professor Edward 
Jackson (Astronomical Geography, p. 3). Three stakes are in 
line, or as nearly in line as is practicable, one mile apart, along 
the shore of a canal or a pond. On these, sighting marks are made 
at a uniform distance above water-level. An engineer's level is 
then placed so that the cross- wires cut the sighting marks of the 
first and third stakes. If the telescope of the level be turned 



THE EARTH AMONG PLANETS 19 

upon the middle stake it will be found that the cross-wires cut 
the stake at a point eight inches below the sighting mark. 





EXPERIMENT TO SHOW THE EARTH'S CURVATURE. 

6 It is by measurements depending on this principle that the 
exact shape of the earth has been ascertained. A pendulum of 
absolute uniform length, weighted by a cannon-ball weighing 
about one hundred pounds, is allowed to oscillate freely. When 
all errors are corrected the rate of vibration will be the same at 
all points of the earth's surface equally distant from the centre. At 
any part nearer the centre, as the poles, the rate of vibration is 
slightly faster ; at any place more remote they will be slower. The 
United States Coast and Geodetic Survey has carried on a series of 
pendulum observations covering a period of many years with the 
results noted on p. 12. Professor Ferrel had shown that, theo- 
retically, the level of the sea between the 20th and 27th parallels 
is about thirteen metres (40 ft.) higher than it would be if the 
earth were a true spheroid. 

7 Any change in the inclination of the earth's axis would have 
the effect of producing decided changes of climate. For instance, 
if the inclination were increased, the limits of the frigid zones 
would be pushed farther toward the equator. That is, if the in- 
clination of the axis were forty degrees instead of twenty- three 
and one-half, the polar circles would each be forty degrees from 
the poles, and the tropics would be each forty degrees from the 
equator. 



CHAPTER II 

THE STRUCTURE OF THE EARTH 

In the long period of time that has elapsed since the 
earth was glowing with intense heat, the substances com- 
posing it seem to have adjusted themselves in accordance 
with the laws of gravitation 1 — that is, the heaviest kinds of 




IDEAL SECTION THROUGH THE EARTH 
The thickness of the "various envelopes is greatly distorted. 

matter are nearest the centre. Structurally the earth con- 
sists of a dense and practically solid globe, the lithosphere, 
nearly covered with a comparatively thin layer of water, 

20 



THE STRUCTURE OF THE EARTH 21 

the hydrosphere or water envelope, the whole surrounded 
by an envelope of gaseous matter, the atmosphere. 

The shape of the lithosphere and the condition of the 
substances composing it, all go to show that in times past it 
was intensely heated, and that much of the rock composing 
it has been iu a molten condition. The globular form is 
the only one that would naturally result from the action of 
gravitation on a plastic or fluid body ; and the flattening 
at the poles is most reasonably explained by the supposi- 
tion of a rotation on its axis while it was still plastic. 

The density of the lithosphere, together with the waters, 
is about that of iron ore a — that is, bulk for bulk, it is about 
five and one-half times as heavy as water. At the surface, 
however, the density of the rocks is not much more than 
half as great ; it is certain, therefore, that the substances 
forming the interior are much heavier than those occur- 
ring at the surface. 

The Rock Envelope. — The outer part of the litho- 
sphere is a shell of more or less friable material called the 
rock envelope, or, popularly, the " crust of the earth." It 
surrounds an intensely heated interior. 3 The rock enve- 
lope itself has lost so much of the heat it once had that it 
is comparatively cold ; the amount of heat it radiates is 
about equal to that which it receives from the sun. 

That the interior of the lithosphere is very hot, however, 
cannot be doubted ; for in every place where the rock en- 
velope has been penetrated by deep borings, a constant 
increase of temperature is observed — the greater the depth 
the higher the temperature. 4 The thickness of the rock en- 
velope is not known, but at a depth of less than forty miles 
it is thought that the temperature is high enough to fuse 
the most refractory substances. The broken folds of the 
outer surface have revealed something of its character to 
the depth of several miles. Borings have been made to a 



22 PHYSICAL GEOGKAPHY 

depth of a little more than a mile (Table II., Appendix), 
but beyond the slight knowledge obtained from these, 
nothing positive is known about its interior. 

The Water Envelope. — About four-fifths of the sur- 
face of the rock envelope is covered by a comparatively 
thin layer of water, the hydrosphere. The water not only 
exists in a free state, at the surface, but in chemical com- 
bination it is a constituent of various kinds of rock 5 that 
occur at or near the surface. 

The waters of the earth form a most important constitu- 
ent so far as life is concerned. Water is an essential ele- 
ment to the existence of life ; for not only does it form the 
greater part of every plant or animal, but it is also the 
chief vehicle by which nutrition is distributed throughout 
the various parts of the body of the animal or the plant. 
Within a range of a very few degrees of temperature, water 
exists in one or another of three forms — a solid, ice ; a 
liquid, water ; and an invisible vapor, often called "steam." 
Water in one or the other of its forms is the agent by 
which, more than any other, the surface of the rock enve- 
lope has been sculptured ; therefore it has a very impor- 
tant part in the science of physiography. 

The Atmosphere. — The atmosphere consists of a mixt- 
ure of gaseous substances — namely: nitrogen, oxygen, 
water vapor, and carbon dioxide. Of these oxygen is the 
substance required in the breathing of animals ; carbon 
dioxide, the gas formed when coal or carbon " burns," is 
essential in the breathing of plants ; nitrogen forms a part 
of the body structure in both animals and plants ; and 
water vapor is the form in which the fresh water is carried 
from the sea to the land. The atmosphere, therefore, is 
just as essential to life as the water envelope. 

The thickness of the atmospheric envelope is not known. 
Various estimates place it between one hundred and two 



THE STRUCTURE OF THE EARTH 23 

hundred miles. At the latter estimate, on a globe one yard 
in diameter, the depth of the atmosphere in proportion 
would be about one-half an inch. 6 Illustrate by diagram. 

Keeping Nature's Balance. — The three envelopes are 
constantly acting and reacting upon each other, and at the 
same time each has certain movements of its own. The 
movements of the rock envelope have changed the level of 
its surface so that the waters are divided from the land, and 
the surface of the land has been wrinkled, crumpled, and 
folded so as to form the plateaus, ranges, and valleys. The 
heat of the sun causes a part of the ocean waters to take 
the form of vapor, and the latter, mingled with the air, 
flows over the land. Being chilled, the vapor again takes 
the form of rain, or of snow, and falling on the land wears 
away its surface. The water gathers into channels and, 
carrying the mingled particles of rock waste in its flood, 
flows back to the sea and there deposits them. 

And so the c} T cle of change ever goes on. At the plane 
where the atmosphere rests upon the land and the sea the 
physiographic processes that modif}" the earth's surface are 
ever in action. 

Vertical Movements of the Rock Envelope. — The 
changes in the surface of the rock envelope that are most 
noticeable are the wearing away of the land and the trans- 
portation of the rock waste to lower levels. That is, 
water falling as rain loosens particles of rock, while 
streams carry it seaward. If the land were everywhere 
level, the run-off of water could wear away but little of it ; 
but vertical movements of the surface that are apparent 
only after long intervals of time are taking place, and 
these, making new slopes, have given the run-off waters 
increased wearing power. 

Movements of the rock envelope in times past have di- 
versified its surface with highlands and lowlands, inoun- 



24 PHYSICAL GEOGRAPHY 

tains and valleys, and similar movements are going on at 
the present time. Probably no part of the earth is free 
from them, but they are most clearly observed along sea- 
shores. Thus, the coast of New Jersey is sinking ; 7 and 




AN UPLIFTED COAST— SAN PEDRO, CAL. 

From a survey made by Merick Reynolds, Jr. The successively formed beaches are shown 

by the strata of shells and sand. 

so also is much of the coast around the Gulf of Mexico, the 
Zuyder Zee, and the delta of the Ganges-Brahmaputra. 
The coast of the New England Plateau has subsided until 
the sea has flooded the coast plain and the lower valleys, 
and has buried most of the old river mouths. The multi- 
tude of bays and fjords that characterize this coast are 
examples of "drowned" valleys. On the other hand, 
parts of the Mediterranean basin, of the California coast, 8 
the Scandinavian peninsula, and the basin of Great Salt 
Lake are rising. 

In nearly every instance in areas to which extensive 
sediments are being carried there is evidence of sinking ; 
while, as a rule, areas that are being denuded are rising. 
It is evident, therefore, that vertical movements of the 
rock envelope — that is, uplift and subsidence — are defin- 
itely connected with the wasting of the land and the trans- 
fer of sediment. 

The cause or causes of these earth movements are not 
known, but it is believed that the gradual contraction of 
the rock envelope to fit itself around a more rapidly shrink- 



THE STRUCTURE OF THE EARTH 



25 



ing interior is the chief cause. There is evidence, too, that 
gravitation is a factor. The removal of great amounts of 
rock waste — often many cubic miles in volume — from one 
locality to another, relieves weight at one place and in- 
creases it at the other. 9 Therefore it is inferred that a 
sinking, because of the increased load, occurs at the latter 
place, and an uplift at the former, on account of the less- 
ened weight. 

The effects of these earth movements are very far-reach- 
ing. The great highland regions of the earth, with their 
ridges and folds, are probably direct results, and it is not 
improbable that the uplift of the continents themselves 
was also due to them. 




IGNEOUS ROCK: A FLOW OF LAVA 



Rock and Its Formation. — To almost every mineral 
substance that forms a part of the earth, the term /'"•/,• is 
applied. Thus, clay, sand, gravel, limestone, quartz, gran- 
ite, lava, and even the fine, wind-blown rock waste, are 



26 PHYSICAL GEOGRAPHY 

each called rock ; and so also is a combination or any mixt- 
ure of them. In many instances there is no doubt at all 
how the rock has been formed, or whether it has been al- 
tered or not, because the whole process of its formation 
has been carried on in plain sight. Thus, when a volcano 
or a fissure pours out a flood of molten lava there is no 
question about how the rock got into place, or whence it 
came. The lava, when it has hardened, may be glassy, or 
metallic in appearance, or it may be like cinder or furnace 
slag ; but there are always qualities about it that deter- 
mine its origin. 

Beyond a depth of a feAV thousand feet from the surface, 
nothing positive is known about the substances of which 
the rock envelope is composed. It is certain, however, 
that most of the rock now at the surface consists of sedi- 
ments carried into place by running water and deposited 
in the form of layers or strata that afterward hardened into 
compact rock. But these sediments must have come from 
somewhere, and there is but one place from which they 
could be derived — namely, from the rock envelope itself. 

Now, no one knows what the 'primitive or first rock that 
formed the crust of the earth may have been, but certain 
kinds of rock have been found underlying the water-formed 
sediments from which the latter seem to be derived. Or- 
dinarjr granite is an example of this kind of rock, and 
granitic rocks are very abundant. There are various 
kinds of granite, but the most common varieties contain 
minerals of which nearly all the elementary rocks them- 
selves are composed. 

One of these minerals is silica, of which quartz and sea 
sand are the best examples. Another is felspar, a mineral 
which, decomposed, yields clay, potash, lime, and soda. 
Another mineral is hornblende, which decomposes mainly 
into iron, lime, and silica. Still another constituent usually 



THE STRUCTURE OF THE EARTH 27 

present is mica, popularly called " isinglass ; " like felspar 
it also decomposes into clay, silica, lime, and a number of 
other substances. 

EXERCISE.— Procure one or more specimens of granite, 10 and with 
the aid of a magnifying-glass observe the following directions. Look 
for small clusters of foliated or " leafy " mineral ; it may be whitish 
or, perhaps, green or brown ; this mineral is mica. If no mica is 
found, look for jet black crystals or masses ; this is hornblende ; it is 
usually opaque, but sometimes translucent. Find the white, trans- 
lucent mineral with glassy lustre ; it is quartz, or silica, and it is apt 
to form the chief bulk of the rock. Look also for an opaque mineral 
varying from yellowish-white to pink in color ; possibly it will break 
into fragments having flat sides, or cleavage planes ; this mineral is 
felspar ; it has different crystalline forms accordingly as it contains 
lime, potash, or soda. 

Igneous Rocks. — There are certain surface rocks that 
have cooled from a molten condition, and of these the 
lavas of volcanoes, though not the most abundant, are per- 
haps the best known. The Hawaiian Islands are mainly 
great piles or domes of lava, and this kind of rock is com- 
mon in most mountainous regions. In many instances the 
molten rock has been ejected from long fissures and has 
cooled slowly ; in this form it is usually known as basalt, 
or, if it breaks into regular blocks, trap. The Palisades of 
the Hudson, Fingal's Cave, and the Giant's Causeway are 
examples. 

All the foregoing are commonly called vulcanic or igne- 
ous rocks ; consult a good dictionary and learn why these 
names are applied. Igneous rocks are usually found in 
mountainous regions, or in localities from which the sedi- 
mentary rock has been removed. Granite rocks prevail in 
the New England Plateau ; igneous rocks are abundant in 
the Western Highlands. 

Sedimentary Rocks. — Although the sedimentary rocks 
that prevail in such a great extent of the land are derived 



28 PHYSICAL GEOGKAPHY 

from the granitic and other vulcanic rocks, there is nothing 
about them to indicate their close relation to the latter. 
The making of firm rock out of loose sediments is a some- 
what complex process. Let us follow the formation of 
sandstone. In the first place the grains of quartz are 
rounded, and in the second place they are uniform in size. 
The rock from which they came, probably granite, has 
crumbled, and water has sorted the various minerals from 
one another. The waves, beating the fragments of quartz 
and rubbing them against one another, have not only 
rounded the grains, but they have also sorted them ac- 
cording to size, and piled them in a nearly flat layer. 
True sand, therefore, is nearly always a formation of beaches 
or of water in motion. 

In time the beach is lifted up above sea-level and cov- 
ered deep with vegetable remains mixed with loam. Water, 
in one form or another, flows over or stands upon the 
surface ; and if the water contains lime in solution it will 
leach through the layer of sand and cement the grains, 
forming sandstone. 

In most instances, clay banks are derived from granitic 
and similar rocks. Felspar decomposes into clay, and the 
latter, being very light and fine, is carried off by the water, 
settling by itself, while the heavier materials remain. In 
many instances the clay is spread over large areas. Pos- 
sibly it remains in the stiff, pasty form by which it is 
commonly known ; more likely pressure, heat, and moisture, 
acting together, convert it into slate. 

It is not difficult to understand how rivers and other 
running waters are active workers in making rock, because 
one can almost always find clay-banks, gravel-beds, and other 
sediments that have been brought down stream and dis- 
tributed by the water. 11 It is not so easy to understand 
how rocks are found at the bottom of the sea ; as a matter 



THE STRUCTURE OF THE EARTH 



29 




SEDIMENTARY ROCK, NEAR OLEAN, N. Y. 
The face of the cliff is one side of a channel of the river. 



of fact, however, probably more sedimentary rock has been 
formed in ocean and lake beds than in any other places. 
In very many instances these rocks are largely composed 
of the remains of animals so small that several thousand of 
them together would not be so large as the head of a pin. 

The sea, especially in regions of warm water, contains 
many thousand species of such animals ; moreover they 
multiply with great rapidity. But the animals are short- 
lived, and as soon as tbey die their bodies sink to the 
bottom. The mineral remains of these organisms consist 
mainly of lime or silica, and in time the thick layer that 
accumulates finally becomes cemented into rock. The 
growth of rock in this way is slow, it is true, but time alone 



30 PHYSICAL GEOGRAPHY 

is required to make such layers of very great thickness. 
The chalk cliffs of England and France were formed in this 
manner, and they aggregate nearly half a mile in thickness. 
The limestones of the Mississippi Valley also accumulated 
on sea-bottoms and have about the same thickness. 

Metamorphic Rocks. — There are many instances in 
which the character of sedimentary rocks has been sub- 
sequently changed. Thus, by pressure and heat in the 
presence of moisture, beds of clay have been transformed 
into layers of gritty slate; chalk and limestone have be- 
come crystalline marble ; and bituminous coal has become 
anthracite. Certain kinds of granitic rock, especially 
gneiss or " stratified granite," are metamorphic. Older 
granitic rock has crumbled, and the rock waste has been 
cemented into firm rock again with but little alteration. 

One might infer, therefore, that the older and deeper 
stratified rocks would be thus changed. 12 This is usually 
the case. The weight of the overlying rock produces im- 
mense pressure, and the changes resulting from the moist- 
ure within them greatly alter their appearance. Many of 
the older rocks, indeed, are much like igneous rock in ap- 
pearance. Bocks that form a part of mountain folds are 
apt to be metamorphic on account of the pressure that 
results from the folding and crumpling. 

EXERCISE.— Procure specimens of clay and slate, chalk (not crayon) 
and marble, bituminous (soft) coal and anthracite. Examine each pair 
with reference to hardness, foliation, crystalline appearance, and den- 
sity (weight of pieces of equal size). Make a list of the rocks occurring 
in the neighborhood in which you live, and classify them as igneous, 
sedimentary, or metamorphic. 

Order of the Strata. — Most of the sedimentary rocks 
were deposited in horizontal layers, but, on account of the 
vertical movements of the rock envelope, they are often 



THE STRUCTURE OF THE EARTH 



31 



found in oblique positions. Sometimes they occur in gen- 
tle folds ; but in mountainous regions they are much 
crumpled and broken. In some of the old sea-beds now 
raised above the surface the strata are undisturbed. 




SEDIMENTARY ROCK: SECTION THROUGH THE CANON OF THE COLO- 
RADO RIVER 

The level of the strata has not been disturbed. 

It is by studying the upturned edges of broken and tilt- 
ed strata that the story of the earth has been read. Each 
stratum is a chapter by itself, and to read the history prop- 
erly it is best to begin with the lowest. It is not always 
easy to tell the relative position of strata at some distance 
from one another, but as each stratum has fossils, or ani- 
mal remains peculiar to itself, the position is usually de- 
termined by the kind and character of these. 




SEDIMENTARY ROCK: TILTED STRATA 

The total thickness of the stratified rocks is estimated 
at upward of twenty miles. There is no locality known, 
and none exists, in which all the various strata are found — 
no locality is known in which even any considerable num- 
ber occur. Not infrequently very old rocks are overlaid 
by those of the most recent formations ; all the intermedi- 
ate strata are missing. 13 

To the lowest strata, that do not differ much from the 
granitic rocks and possibly include some of them, the name 



32 



PHYSICAL GEOGKAPHY 



Archcean u is given, 
the continents and 





They seem to be the foundation of 

the floor of the oceans. The decay 

and wearing away of these has 

formed the material of which 

- nearly all the sedimentary rock 

|§ is composed. " The waste of the 

| old land is the material of the 

11 neiv." 

The remaining strata are 
named in accordance with the 
character of the life forms that 
existed when the rocks that 
compose them were undergoing 
formation. Upon the Archaean, 
rest the rocks of the Palceozoic 
era — the age of the earliest life 
forms. Then follow the rocks 
of the Mesozoic, or middle-life 
era; the Cenozoic, or era of re- 
cent life ; and, last of all, the 
era of man. 

Archaean Era. — In Archaean times North America con- 
sisted mainly of a narrow, V-shaped strip of land south of 
Hudson Bay. The crests of the Appalachian Mountains 
were just above the sea level ; the Black Hills and one or 
two peaks of the Rocky Mountains had also just emerged. 
The general form of the American continent was outlined 
in Archaean times. With the possible exception of a few 
species resembling the sponge, no forms of life are found 
in Archaean rocks. (See illustration, p. 34.) 

Palaeozoic Era. — The Palaeozoic era was of very long 
duration. The sediments composing it are 25,000 feet 
thick in places. The greater part of Europe and North 
America were above sea-level during this period, but the 



UNCONFORMABLE STRATA : 
CANON OF THE COLORADO RIVER 

The tilted strata, originally horizontal, 
were deposited on the surface of the 
igneous rock. Subsequently the upper 
layers were deposited on the broken 
surface of the tilted layers. 



THE STKUCTUEE OF THE EARTH 



33 



land was many times 
upheaved and sub- 
merged. In North 
America the greater 
part of the Mississip- 
pi Valley was a shal- 
low inland sea, that 
later became an im- 
mense marsh. 

In the variety and 
extent of life forms 
the Palaeozoic era is 
the most noteworthy 
of all the geological 
periods. It began 
with the lowest form 
of sponges and closed 
with the advent of 
mammoth reptiles. 
During this period an- 
imals with backbones 
appeared for the first 
time. Insects Avere 
numerous, and toward 
the close reptiles ex- 
isted. Fishes and 
mollusks seem to have 
been the prevailing 
forms. 

The climate was 
warm and moist. The 
vast accumulations of 
vegetable matter that 
are now the coal fields 



$1 




S* 5 

as" 






2"= 
©S 




Quaternary ] Champiaii 
(■ Glacial 



Tertiary 



Cretaceous 



Jurassic 



Devonian 



Silurian 



Cambrian 




ORDER OI- STRATA 



34 



PHYSICAL GEOGEAPHY 



were found in swamps of this age. 15 In North America 
these swamps covered much of the area that is now the 
central United States. 

Mesozoic Era. — During the Mesozoic era both North 
America and Europe had grown to about their present 
shape. In the former division the Gulf of Mexico reached 



as 



far north as the mouth of 



the Ohio, and a north- 
western branch of it ex- 
tended nearly to the 50th 
parallel. In Europe all 
the principal mountain 
ranges 16 and the higher 
elevations of land most 
probably had been raised 
permanently above sea- 
level. 

It was an age of gigan- 
tic reptiles. The animals 
of some species were from 
sixty to eighty feet in 
length. Eor the first time 
birds appeared. They 
were very much like rep- 
tiles, however, and in 
some species they had, instead of horny beaks, heavy jaws 
with socket teeth. 

Cenozoic Era. — This era was largely one of uplift and 
mountain-making, although both in North America and 
Europe the various ranges and systems had received defi- 
nite forms. The former was a continent of vast fresh-water 
lakes ; the latter of inland seas. 

Most of the life forms that flourished in preceding ages 
were common, but one great step in advance maybe noted 
— the appearance of mammals. Their genera included 




NORTH AMERICA IN ARCHAEAN TIMES 

The shaded area shows the part of the continent 
above sea-ienjel. 



THE STRUCTURE OF THE EARTH 



35 




the elephant, camel, 17 rhinoceros, wolf, deer, and horse. 13 
There was a considerable advance in plant-life, and the 
forest trees both of North 
America and Europe in- 
cluded most of the sjDe- 
cies found to-day. 

Quaternary Age. — 
The abrupt close of the 
Cenozoic era was prob- 
ably due to an elevation 
of a large part of North 
America and Europe from 
1,000 to 2,000 feet, and a 
decided lowering of tem- 
perature. The ice and 
snow of the north polar 
regions crept southward 
until it enveloped nearly 
all of Europe and the 
greater part of the United 

States. This accession of ice is commonly known as the 
glacial epoch. It is marked on a stupendous scale by a 
movement of drift similar to that which marks the gla- 
ciers of the present time. 

The changes of the Quaternary age were disastrous to 
life. In the area covered by glacial ice most of the spe- 
cies of larger mammals perished. The cave bear, horse, 
wolf, and reindeer survived. Many species of plants were 
destroyed, but many escaped. 

That man existed before the close of the glacial epoch 
seems certain. In the caverns of Belgium, Germany, and 
Italy the bones of man have been found in caves along 
with the skeletons of animals and various implements of 
the chase. From the few scraps of unwritten history it 



NORTH AMERICA IN CENOZOIC TIMES 

The shaded area shows the part of the continent 
above sea-level. 



36 



PHYSICAL GEOGRAPHY 



seems that primitive man was a savage of the lowest type. 
He lived in caves and obtained his food by hunting and 
fishing. He did not cultivate the soil nor did he have any 




THE UNITED STATES AT THE BEGINNING OF THE QUATERNARY AGE 
The shaded area shows the part added in recent times. 

domestic animals. He had learned the use of fire, how- 
ever, and from that moment his intellectual development 
was a question of time only. 

QUESTIONS AND EXERCISES.— A mixture of iron filings, sand, 
and meal is gently shaken in a glass : what position will the compo- 
nents take when they come to rest ? Explain why. 

It is sometimes assumed that the rock envelope is about forty miles, 
and the atmosphere about two hundred miles, in thickness. Construct 
a diagram on the blackboard or on paper, showing the relative thick- 
ness of each on scale in the ratio of 4000 : 40 : 200. 

Obtain specimens of iron ore, marble, and dry clay, and compare 
the weight of pieces of the same size. If possible find the specific 
gravity of each. Determine, or judge by " hefting," the relative weight 
of the various kinds of rock in the neighborhood in which you live. 

Note and describe any instances within your personal knowledge of 
the action of water on the rock envelope ; explain the nature of the 
changes and how they have been brought about. 

Study the various rock formations in the neighborhood in which you 
live and classify them according to their origin— that is, as sediment- 
ary or igneous. 

Make a collection of them for future use. 



THE STRUCTURE OF THE EARTH 37 

A stream flows over a bed of limestone rock that is slightly soluble, 
into a lake without an outlet ; what changes in the formation of 
rock are likely to occur ? Will the rock formed be stratified or un- 
stratified ? In what way may it become fossiliferous ? 

From the official State reports find the order and distribution of rock 
strata in the State in which you live, and from the information given 
construct a geological map. 



COLLATEEAL READING 

Powell.— Physiography of the United States, pp. 22-29. 
Le Conte. — Elements of Geology, pp. 127-132. 
Mill.— Realm of Nature, pp. 211-230, 249-261. 
Shaler. — First Book of Geology, pp. 107-124. 



NOTES 

'That is, the substances specifically heaviest are nearest, and 
the lightest are farthest, from the centre. 

2 Iron and its compounds form one of the most abundant con- 
stituents of the earth, and it is likewise one of the most abundant 
substances of the sun and of some of the fixed stars. All the me- 
teorites that have landed on the earth contain it, and in most of 
them it is the chief element present. 

3 It must not be inferred from this, however, that the heated in- 
terior is in a liquid condition ; on the contrary, the earth be- 
haves like a solid but somewhat elastic body. The melting or 
fusing of a substance depends not on temperature alone, but on 
pressure as well. With increase of pressure, the temperature of 
fusion is also raised ; and the great weight of the overlying rock 
may possibly produce a pressure great enough to prevent lique- 
faction. 

1 The increase varies not only in different localities, but in dif- 
ferent kinds of rock, the average being one degree for each sixty 
or seventy feet, In a certain boring in Upper Silesia, 6,700 feet 
deep, there is a slight decrease in the ratio, but a marked in- 
crease in the actual temperature at the greater depths. 

6 The crystalline form of many rocks is due to the water they 
contain in chemical combination, and there are but few rocks of 



38 PHYSICAL GEOGKAPHY 

which water does not form a considerable part. It is by no means 
impossible that the waters of the earth, in time, may be absorbed 
in this way, disappearing as free water, to reappear in chemical 
combination. 

s About one-fifth of the atmosphere consists of free oxygen, an 
element that forms also about one-half the weight of the earth's 
crust, so far as can be estimated. In time, possibly, all the free 
oxygen will be absorbed, entering into chemical combination with 
other substances. 

7 In most instances the rate of sinking is about equal to the 
depth of the layer of sediment annually spread over the surface. 
The amount of sediment carried into the Gulf of Mexico is enor- 
mous, but it does not apparently raise the level to any great ex- 
tent ; few parts of the made-land surrounding the gulf are more 
than ten or fifteen feet above sea-level. 

8 At San Pedro, California, the upward movement has been un- 
usually rapid. Several layers of shells mixed with sand are found 
one above another, at heights varying from five to fifteen feet or 
more. The shells belong to species some of which are not now 
extinct, and most of them have been preserved in their natural 
state. The highest beach is nearly three hundred feet above sea- 
level. The various beaches are so slightly weathered that they 
seem scarcely altered. (See illustration, p. 24.) 

9 According to this principle the rock envelope of the earth 
always maintains a state of balance, adjusting itself to the load 
it carries. It is readily illustrated by putting an ounce weight 
on an inflated toy balloon. The surface of the balloon is de- 
pressed by the weight, but if the latter be removed the surface 
again rises ; or if the weight be moved from one part of the bal- 
loon to another the surf ace at the one part rises while at the other 
it sinks. 

10 Normally, granite is a mixture of mica, felspar, and quartz. 
If it contains hornblende instead of mica it is called syenite ; if 
both mica and hornblende are present it is syenitic granite. If 
the felspar contains soda the granite is diorite. If the rock 
shows layers it is then called gneiss. 

11 An interesting example of rock-formation occurs at Sweyney 
Cliffs, Shropshire, England. A small stream of water pours over 
a red sandstone cliff, mainly in the form of a rapid. The water 
contains a considerable proportion of lime and magnesia ; and a 



THE STEUCTUEE OF THE EAETH 39 

species of coarse moss grows freely in the saturated earth about 
the stream-bed. The mineral salts of the water are deposited co- 
piously on the moss, and little by little the latter, together with 
the other matter entangled, has become so completely incrusted 
that it forms a dyke about twenty feet wide. The dyke stands 
out, having built itself from the edge of the cliff a distance of ten 
feet or more. About three cubic yards are added each year. 

'" Substances ordinarily insoluble in water are quickly changed 
when subjected to water under a high temperature. If a thick 
steel tube, filled with water and fragments of granite, be intensely 
heated for several hours, the larger part of the rock will be dis- 
solved. Hot alkaline water will also dissolve granitic rocks, the 
dissolved matter being precipitated when the water cools. 

13 Thus, the rocks of the Mississippi basin belong to a very old 
and remote geological period. They are overlaid by a thin cover 
of rock waste that belongs chiefly to the most recent period. 

14 The word Archaean means "the beginning" ; Palaeozoic is 
derived from two Greek words meaning " early life " ; llesozoic, 
similarly, is "middle life''; and Cenozoic, "recent life." The 
Silurian age was named from " Silures, " a former name for the 
people of Wales; Devonian comes from "Devon," England; 
Huronian, from "Huron"; and Laurentian from "St. Law- 
rence." All these names are derived from the localities in which 
the rocks were first studied. 

16 Coal measures are not confined to the Carboniferous age ; they 
occur in all geological ages. Thus, the coal fields of the Pacific 
coast belong to the Tertiary age. Those of the Carboniferous 
age, however, are so vast in extent that they overshadow all 
other features. 

1C The uplift of the Pyrenees Mountains did not occur until 
nearly the end of Mesozoic times. 

17 There were several species of camel during these times. It 
is interesting to note that this animal, now confined to the east- 
ern continent, was a native of the west. 

18 The earliest species of horse had, instead of one, five toes. In 
subsequent times two of these gradually disappeared. The horse 
of modern geological times has but one toe, but the "splint 
bones ' ' just above the hoof are the toes of the Quaternary horse. 



CHAPTEE III 



LAND AND WATEE, AND THEIE OUTLINES 



The surface of the rock envelope is not smooth, nor is 
any considerable part of it perfectly level, as the word is 
commonly used. More than three-fourths of its surface is 
covered by the sea, but the remaining part consists of very 
irregular areas that are 
higher than the level of 
the water. The great 
body of water that covers 
so much of the rock en- 
velope is the sea ; : the 
areas above sea-level 
constitute the land. The 
lowest part of the rock 
envelope below sea-level 
— that is, the lowest part relative areas oh land and water 
of the sea-bottom — is 

about five and one-half miles, and the highest point above 
it is just about the same distance. The average elevation 
of the land is not far from 2,000 feet, but the average 
depth of the sea is about 2,000 fathoms. 

The land aggregates about 53,000,000 square miles. It 
clusters around the north pole, and from this circumpolar 
region it radiates toward Cape Horn, toward the Cape 
of Good Hope, and toward Tasmania. In which hemi- 
sphere is the greater part ? Which of the two temperate 

41 



OCEANIC AREA 




C ONTI NE NT/VL 
AREA 












□ 






ISLANDS 





42 



PHYSICAL GEOGKAPHY 



zones includes the greater area ? How many great land 
masses, each surrounded by water, are there ? The two 
largest masses are divided nearly in twain, each at the 
central part, 2 and the smallest is separated by an arm of 
the sea which seems to have severed it from the largest. 
The three largest land masses are called continents ; 3 the 
smaller ones islands. The line along which the land and 
the sea meet is the shore ; the narrow strip of land nest 
the shore, the coast. 

The Continents. — The continents are so called on ac- 
count of certain features of their structure. Each one, for 
convenience, is divided into grand divisions, and the latter 



<c 








Id 

Q. 












z 


SOUTH 


NORTH 




O 












< 


AMERICA. 


AMERICA 


AFRICA 


a. E 


U 


R 


A 


S 


A 


u 








D 























































RELATIVE AREAS OF THE CONTINENTS AND GRAND DIVISIONS 

are also conveniently called continents. In general, the 
continents have a high border on one side and a lower one 
on the opposite side. They are variously named, but they 
are usually styled the Eastern, or Asian ; the Western, or 
American ; and the Australian. The shore of a great 
body of land in the south circumpolar regions is known 
to exist, but practically nothing is known of its extent. 

In a previous chapter it has been noted that changes in 
elevation, especially along the shore, are taking place. 
The real extent of the continents, therefore, is not appar- 
ent ; in many places it comprises an area somewhat greater 
than the part above water. Each is surrounded by a 
margin, varying from a few rods to one hundred miles or 
more, upon which the sea is comparatively shallow ; be- 



LAND AND WATER 43 

yond this margin the surface slopes rather abruptly iuto 
deep water. 

The submerged margin is very generally considered a 
part of the continent. The depth of water along its extent 
varies, and in places the margin itself reaches above sea- 
level. The margin of each continent is more or less con- 
tinuous, and forms a high surface in comparison with the 
surrounding sea-bottom. It is usually called the continental 
shelf.* The map on p. 45 shows both the highland and the 
lowland regions of each continent and also its submerged 
shelf : facing what ocean are the highlands ? — the lowlands? 
Where is the continental shelf widest? — on which side of 
North America has it the greatest width ? The highlands 
are represented by the area above the level of 2,000 feet : 
compare the extent of highlands and lowlands in each con- 
tinent ; in North America. Are the highlands continuous 
or broken ? Each one is a great plateau rimmed and trav- 
ersed by lofty mountains. About one-fifth of the Austra- 
lian, two-fifths of the American, and three-fifths of the 
Asian continent are above the 2,000-foot contour. 

The altitude of the highest regions of the continents 
differs much. The greater elevations of North America 
are from one to one and a half miles above sea-level ; 
those of South America, about two miles ; and the highest 
parts of Asia are more than three miles above sea-level. 
The mountains that rim or surmount the highlands are 
much higher — in many instances about twice as high. 

The slopes toward the Arctic and Atlantic Oceans are 
long and gentle ; how does this fact compare with the 
slopes of the Pacific and Indian Oceans? As a rule, the 
lowland regions are more nearly level than the highlands. 
On which side of the eastern continent are its principal 
lowlands ? On which side of the American continent are 
they situated ? 



B 



THE WORLD 

showing 

ELEVATION OF LAND 

and 

DEPTH OF WATER. 



A/Sfo 



Elevation of Land 

H 20,000 Feet 01 over 
10,000 - 20,000 Feet 
1,000 - 10,000 " 
0- 1,000 " 
I I telow sea level, 

Bei>th of Water 

- 1,000 Fathoms 

1,000- 2,000 " 
2,000- 4,000 " 
4,000 or over 



46 



PHYSICAL GEOGKAPHY 



The mean elevation of the land varies considerably in 
the various continents. If their surfaces were levelled off 
Australia and Europe would be not far from one thousand 
feet high ; North America and Africa about two thousand 
feet ; and Asia nearly three thousand feet. Africa would 
be probably a little higher, and South America not quite 
so high as North America. 

In a few instances there are depressions in the land be- 
low sea-level. The surface of the Caspian Sea is eighty -four 
feet below that of the Mediterranean ; the Dead Sea, situ- 
ated in a gash north of the Red Sea, is thirteen hundred feet 
below sea-level. There are two small depressions in North 
America, north of the Gulf of California ; and two or three 
in Africa, south of the Atlas Mountains. It is not unlikely 
that these were former arms of the sea that were severed 

from the main body. 

Islands.— The islands 
have an aggregate area 
of about three million 
square miles, or about 
one-seventeenth of the 
entire land surface of the 
earth. The majority of 
them are situated on the 
continental plateau, and 
are at no great distance 
from the continents to 
which they belong. Many 
of them are partly sub- 
merged ranges of moun- 
tains that are parallel to 
the maritime ranges of 
the continent, or that ex- 
tend from it. Find two 




A STRETCH OF THE COAST OF NORWAY 

The coast, deeply indented with fjords, is bordered 
by many thousand rocky islets. 



LAND AND WATER 47 

such chains near the American continent, two near the 
Asian continent. Islands of this character are usually 
called continental islands ; and the reason is obvious. 

In a few instances, here and there, are islands far distant 
from any large body of land. There is no doubt about 
the origin of some of them ; they consist of the lava that 
has been ejected from volcanoes. In some instances these 
islands are solitary, as Jan Mayen and St. Helena ; in 
others they form a chain, as the Hawaiian group. 

In the Pacific Ocean there is a large area in which isl- 
ands are so numerous that they form the well-defined grand 
division Polynesia; find the meaning of this word from 
the dictionary. These islands occur in quite regular chains 
that are roughly parallel in direction ; they are therefore 
thought to be the higher summits of submerged mountain- 
ranges. In some instances a volcanic peak is in sight, but 
for the greater part the position of each peak is marked 
by the reef of coral growth that encircles it. The islands 
themselves are popularly known as coral islands. 5 

It has been inferred that the coral polyps began their 
growths on the slopes of the volcanic peaks, and that the 
latter gradually subsided until they were covered by the 
sea. But while the peak was slowly sinking the coral 
polyps steadily built their reefs upward, keeping the top 
always even with the wash of the waves. This opinion, 
first made prominent by Darwin, is borne out by the fact 
that, while the coral polyp cannot live more than twenty 
fathoms below the surface of the sea, the reefs sometimes 
extend almost vertically to a depth of several hundred 
fathoms. 

A peculiar feature about many of these islands is their 
form. As a rule each consists of an irregular ring of reef 
matter, broken and tossed up by the waves, surrounding 
shallow water. The reef is called an atoll ; the enclosed 



48 PHYSICAL GEOGRAPHY 

water a lagoon. Usually the atoll is broken in one or more 
places, and in many instances the lagoons form good Iiar- 

.__ bors. The reef is rarely more than a 

/V::: \ few feet high, and its vegetation is con- 

/ i;-j : /' \ fined to a few species, mainly of palms. 

/ a li, \ The Sea. — The sea covers more 

/ | % \ than half the northern and about 

o " \ seven-eighths of the southern hemi- 

'-'■••' '■ •«. • sphere. Although the area it covers 

ip£ m ° y w\ is continuous, it is separated by the 

*•*"* J 3.1 continents into great divisions called 

r? \ * I oceans. Name them. Which one is 

f'V" V / nearly enclosed ? Compare the At- 

&/ lantic m shape with the others. For 

^j convenience, the polar circles are 

| taken as the boundaries of the polar 

I f ..••••■ I oceans, and the equator convention- 

\ / ally divides the two largest oceans 

\ '•...•"•'' ... / into northern and southern divisions. 

\ : 'i. / Which of the oceans is nearly land- 

\, J locked ? At what place do the Pacific 

a group of coral and Arctic Oceans meet ? the Atlan- 

^° A LL R S AR S ^° R U F N F D F ED tic and Pacific? the Atlantic and 

BY A BARRIER REEF 

Indian ? the Atlantic and Arctic ? 

The Pacific Ocean comprises about one-half the entire 
Sea ; the Atlantic about one-quarter. The shore line of 
the latter, however, is considerably longer ; explain why. 
Why are not the polar oceans important routes of traffic ? 
On a globe trace a northwest passage from London to 
India ; why is not such a passage feasible as a trade route ? 

In general, the average depth of the oceans varies with 
their size — the larger the ocean the greater its depth. The 
Pacific is about 2,500 fathoms, the Atlantic and Indian not 
far from 2,000 fathoms. The polar oceans are shallower, 



LAND AND WATER 49 

but not enough is known about their depth upon which an 
average can be computed. The greatest ocean depths are 
much in excess of the average depths. There is a large 
3,000-fathom area in the north Pacific — compare it with 
Australia in size — and several smaller areas in the Atlan- 
tic and Indian Oceans. There are also several 4,000-fathom 
and at least two small 5,000-fathom areas ; describe their 
positions. 6 The greatest depth of the sea, it is seen, 
scarcely surpasses the height of the loftiest mountain 
peak ; yet while four-fifths of the sea basin is six thou- 
sand feet lower than sea-level, less than a tenth of the land 
reaches six thousand feet above it. 

The floor or bed of the sea is by no means so irregular 
as the surface of the land ; and, the vicinity of the coral 
islands and the continental shores excepted, no steep slopes 
or abrupt changes of level are known to exist. The sound- 
ings made for the telegraph cables disclosed no slopes nor 
inclines too steep for a railway grade. After deep water 
was reached, the soundings for the Atlantic cable of 1866 
did not vary more than seven or eight hundred feet in two 
thousand miles. 

Arms of the Sea. — In various places the sea extends to 
a considerable distance within the general outlines of the 
continents, forming the bodies or arms called seas, gulfs, 
bays, sounds, straits, etc. Many of the smaller coves and 
estuaries are shore formations, having been made or 
shaped by the action of waves or by currents of water. 
The larger arms, however, are structural, and have resulted 
from upheaval or depression of the continent, or of some 
part of it. 

The borders of a continent may be flanked by lofty 
highlands, and the trend of the coast usually conforms to 
the trend of the ranges. Thus, the bend that gives the 
west coast of Africa its shape also gives a similar form to 



50 



PHYSICAL GEOGKAPHY 



the Gulf of Guinea. Where parallel ranges extenci sea- 
ward, or form an angle with the coast, the sea usually en- 
ters the valley to some distance between them. On a map 
of North America, note the position of the Gulf of Cali- 
fornia, and Puget Sound ; on a map of Europe, the Adri- 
atic Sea. Note similar examples along the west coast of 
Asia. Compare the coast lines of the grand divisions 
with reference to indentations. Which has the longer 
coast line — Europe or Africa ? 




A ROCK-BOUND COAST : THE CYCLOPS, COAST OF SICILY 
Unfit for commerce and a menace to navigation. 

Almost any partly enclosed portion of an ocean is called 
a sea, and the Caribbean and North Seas are examples of 
a type of enclosed waters. There is another type, how- 
ever, that is even more remarkable because practically 
land-locked. Of this type the Mediterranean is an exam- 
ple, and such arms of the ocean are now often called medi- 
terraneans. The Gulf of Mexico is properly included in 
this class. Nearly all the larger arms of the sea are de- 



LAND AND WATEE 51 

pressed parts of the continents, or of the plateau on which 
they are situated. 

Coast Forms. — The study of almost any good map of 
a continent, or of any considerable part of its shore out- 
lines, shows that various parts of the coast differ materially. 
Compare, for instance, the coasts of Maine and Florida ; 
of the Chesapeake Bay and southern California. The illus- 
trations on pp. 46 and 52 are examples of shore forms. 
One of them is a rock-bound coast deeply indented with 
fjords and hemmed in by rocky islets. This coast has 
been worn and frayed by the action of sheets of ice, but it 
has also subsided until the valleys are submerged by the 
sea. Name the various coasts that resemble it. 




A CLIFF-GIRT COAST : SAN JUAN, PUERTO RICO 

In the illustration on p. 52, the plain bordering the sea 
dips so gently below sea-level that the water is shallow half 
a mile or more from the shore. The drag of the waves roll- 
ing in and combing on the coast picks up sand and rock 
waste brought down by muddy streams and piles it in the 
form of long spits and beaches at a little distance from the 
shore. 7 Find other coasts that resemble it. 



52 



PHYSICAL GEOGKAPHY 



Along many parts of the coast the sea seems to be en- 
croaching on the land, and the waves beat against the 
shore, breaking it away until there is a high cliff with a 
narrow beach at its foot. A considerable extent of the 
California coast is bordered by sea-cliffs, and they occur 

here and there along the 
North Atlantic coast, as 
at the coast of Newport, 
Rhode Island. 

Coral formations are 
very important factors in 
shore lines. On shore 
they are called fringing 
reefs ; farther out, bar- 
rier reefs. Almost the 
entire east coast of Aus- 
tralia is shut off from 
open communication by 
a barrier reef more than 
twelve hundred miles 
long. There are a few 
channels across the reef, 
but the latter is a great 
obstacle to commerce. 
Fringing reefs occur on 
the south coast of Flor- 
ida, and they are per- 
haps the most common 
examples of coral formation. They are common along 
the shores of the Bahama Islands, and occur here and 
there along the Hawaiian coast. 

Coral growths are confined to warm, littoral waters, and 
the reef-building polyp is limited to waters whose temper- 
ature does not fall below 25° (67° F.). Absolutely clear 




A STRETCH OF NORTH CAROLINA COAST 

The barrier beaches nearly enclose the coast ; the 
inlets are kept deep enough for navigation by the 
tidal currents. 



LAND AND WATER 53 

water is requisite, and for this reason coral reefs are rarely 
found along the shores of continents, and never within the 
reach of river sediments. 

Coast Outlines and Civilization. — The coast forms of 
a country have not a little bearing on its prosperity and 
its enlightenment as well. A coast with good harbors in- 
vites commerce and intercommunication. Along the North 
Atlantic coast of the United States, where a rugged surface 
slopes abruptly below sea-level, good harbors are nume- 
rous. The same conditions prevail on the coast of Europe. 
Of two regions, one having good, the other poor harbors, 
commerce and intercommunication will seek the former. 
Africa and South America have but very few good harbors, 
and to this fact the half-savage condition of the native 
peoples is largely due. The great stride in the progress 
of the Japanese people was begun when they opened their 
ports to foreign trade. 

QUESTIONS AND EXERCISES.— How have good harbors affected 
the progress of the English people ? What has been the effect of closed 
ports on the Chinese ? 

Compare the commerce of the North Atlantic coast of the United 
States with that of the South Atlantic coast. To which type does each 
of these coast forms belong ? Where are most of the large seaports of 
the Atlantic coast of the United States ? Explain the reason for their 
location. 

Why should Australia be considered a continent rather than an 
island ? 

Does the cutting of the Suez Canal give Africa any insular properties 
that it did not possess before ? 

Make a list of the principal mediterranean seas of the world. 

Mention several instances in which peninsulas enclose waters so as 
to form gulfs or bays. 

From a good map of the British Isles find the names used as syno- 
nymes of " cape " and " strait." 

Find the centre of each hemisphere on p. 40. 

Study the position of the submerged part of the continents on the 
map, pp. 45-46. 



54 PHYSICAL GEOGRAPHY 



COLLATERAL READING 

Dana. — Manual of Geology, pp. 145-152. 

Redwat. — New Basis of Geography. Chapter IV. 

Shaler. — Sea and Land, pp. 1-87-222. 

United States Geological Survey. — Norwich and New 
London Sheet (drowned valleys) ; Sandy Hook and Barnegat 
Sheets (spits and barrier beaches) ; Port Washington Sheet 
(cliffs). 

NOTES 

1 It is commonly asserted that the same amount of water ex- 
ists on the earth at the present time as during remote geological 
periods. This is doubtless true, but it is also true that not all 
the water is in the same form now as in prior times. When 
the earth was younger there was much water in a liquid form 
that is now chemically combined with various mineral elements. 
Nearly all the minerals, especially those in a crystalline form, 
contain notable proportions of water in combination. 

2 This separation of the land masses has been aptly called 
the "zone of fracture." The isthmus of Panama is scarcely 
thirty miles wide and the isthmus of Suez is only one hundred 
miles across. Yet these two necks of land are all that connect 
the divisions of each continent. That is, twenty-five thousand 
miles of open navigation are obstructed by less than one hundred 
and thirty miles of land. Even these barriers are disappearing 
because of canals either completed or projected. 

3 It is now the custom to restrict the latter term to the largest 
land masses, but it is sometimes more convenient to apply it to a 
grand division. Europe and Asia are also called continents, but 
the only real boundary that separates them is the desert high- 
land that separates western from oriental civilization. Physically 
it is better to treat Eurasia as a whole — politically and histori- 
cally the two divisions are best considered separately. 

4 This margin is also called the continental plateau, the conti- 
nental border, and the submerged border. 

5 The coral polyp is a zoophyte form of marine animal growth 
not unlike a tree with its branches. The mouths of the polyp 



LAND AND WATER 55 

completely cover its upper surface in much the same manner as 
the flowers of the hollyhock or mullein cluster about the stem. 
In a single community the growth of the polyp is chietly upward, 
but where the communities are thickly clustered, their branches 
interlock and finally form a compact mass. The living portion 
of a coral is found at the surface of the water or a few feet below 
it ; the dead portion may extend a hundred fathoms or more be- 
low the surface. 

6 The deepest soundings so far obtained are 4, 655 fathoms by the 
TJ. S. S. Tuscarora, east of Japan, in an area now known as Tus- 
carora Deep ; 5,147 fathoms, one hundred miles E. N. E. of Sun- 
day Island ; and 5,155 fathoms a few leagues east of Macarthy Isl- 
and, not far from the Kermadec group. The two last were made 
by Commander Balfour, H. M. S. Penguin. North of Puerto Rico 
a sounding of 4,651 fathoms has been obtained. The cable ship 
Nero reported a sounding of 5, 200 fathoms east of the Hawaiian 
Islands. Formerly deep sea soundings were made with heavy 
Manila rope, and in very deep water it was impossible to tell 
when the sinker had reached bottom. With the method perfected 
by Admiral Belknap and Captain Sigsbee, steel piano wire takes 
the place of the rope. The wire carries at its lower end a sinker 
which detaches itself on touching bottom, at the same time clos- 
ing a cup that secures a specimen of the bottom. Very few of 
the deep-sea soundings made prior to 1870 are now considered 
trustworthy. 

7 Marine currents frequently attempt to carry away the rock 
waste piled up by the waves, and between the two it is dragged 
into a curved form making a hook. Sandy Hook, New Jersey, 
is an example, and similar examples are found along the shoree 
of Martha's Vineyard and Nantucket. 



CHAPTER IV 

THE KESULTS OF SLOW MOVEMENTS OF THE EOCK 
ENVELOPE: PLAINS, PLATEAUS, AND MOUNTAINS 

The larger vertical forms of the land are the results of 
the slow movements of the rock envelope. Any consider- 
able area of land but little higher than sea-level is called 
a plain; if considerably higher, a plateau ; if wrinkled, 
folded, and broken, a mountain system. There is no fixed 
elevation at which an area ceases to be a lowland, or vice 
versa, but in general, surfaces more than two thousand feet 
above sea-level are called highlands, while those of less alti- 
tude are lowlands. 

As a rule, the various features that constitute topogra- 
phy are distinct one from another ; but in many instances 
lowlands gradually increase in altitude and become high- 
lands ; an almost imperceptible swell in a level plain may 
develop into a cliff or a ridge ; and a mountain-range, little 
by little, may lose its characteristic form among other 
features of the landscape. So it often happens that a sin- 
gle topographic form may have the character of several 
kinds of relief. 

Plains. — Any level or nearly level stretch of land is 
commonly called a plain. Most plains are lowlands, but in 
a few instances the name is applied to surfaces that are 
more than six thousand feet above sea-level — an elevation 
considerably greater than that of some mountain-ranges. 
The plain east of the Rocky Mountains is an example ; 

56 



PLAINS, PLATEAUS, AND MOUNTAINS 57 

it is higher than the crests of the Appalachian Mountains, 
and about as high as the highest peaks. 

Plains are variously named. The grassy plains of the 
New World were named savannas by the Spanish, and 
prairies by the French — both of which names are very 
commonly employed. In South America the vast plains 
of Argentina are called pampas ; the grassy plains of the 
Orinoco, llanos ; and the forest-covered plains of the Ama- 





A ROLLING PLAIN, VIRGINIA 
The forestry is deficient, and the soil only moderately fertile. 

zon, silvas. 1 In Eurasia, the vast plains that almost girdle 
the Arctic Ocean are known as steppes, their frozen, swampy 
coast fringe being known as tundras. In England and 
Scotland the terms, meadow, heath, and moor, are used. 

Origin of Plains. — Most plains have been formed by 
the action of water, or have received their surface configu- 
ration by it. If shaped by comparatively still water they 



58 PHYSICAL GEOGKAPHY 

are known as marine or lacustrine plains ; the former being 
old sea-bottoms ; the latter lake basins. If formed of sedi- 
ments deposited by running streams they are alluvial 
plains ; if levelled off by moving ice, diluvial plains ; if on 
the margin of the sea or a lake, 'coast plains. 

Marine and lacustrine plains constitute by far the greater 
area of the lowland surface of the earth. Originally old 
sea or lake bottoms, their surfaces are level, because the 
sediments forming them were deposited in still water. In 
some instances the floor was filled and levelled off by the 
remains of minute animals ; in others by dead and decay- 
ing vegetation. 

In time these old bottoms were raised above water-level 
and, if their surfaces were not wrinkled and folded, they 
constitute the plains of to-day. Thus, the larger part of 
the Great Central Plain of North America is an old sea- 
bottom, and so, too, is most of the great northern plain of 
Eurasia. Of lacustrine plains, one of the finest examples 
is the valley of Red River of the North. This plain re- 
sulted from the draining of a lake, and was so recently 
formed that its surface has scarcely been notched by the 
river that now imperfectly drains it. 

The plain surrounding the Caspian Sea is an excellent 
example of a plain in the process of formation. On the 
northern side, the gradual shrinkage of the lake has left a 
plain more than two hundred miles wide, and when at 
length the lake disappears, a broad, wind-swept plain will 
take its place. 2 The valley or basin of Great Salt Lake 
possibly is passing through a similar period of growth 
and development. 

Alluvial plains are usually best developed along the 
lower courses of rivers, although they exist in narrow 
reaches along almost the entire length of the stream. The 
bottom-lands of the lower Mississippi and the Danube ; 



PLAINS, PLATEAUS, AND MOUNTAINS 59 



the mazy deltas of the Nile and the Ganges-Brahmaputra, 
and the broad, fertile plains of the Po are examples. 3 
Name other illustrations. 

The surface of a coast plain is made level by the action 
of the waves, and if an uplift of the surface is taking place, 
the plain gets gradually wider and wider as successive por- 
tions of the sea-bottom are brought to the surface. The 
coast plain along the South Atlantic and Gulf coast is an 




A LEVEL PLAIN, KENTUCKY 
A very fertile prairie with considerable forest growth. 

excellent example. 4 Much of the material of which it is 
composed is sediment brought down by the rivers, but the 
waves have been the chief agent in building it. Through- 
out its whole extent it is but little higher than tide-water. 
The line along which the coast plain joins the older land is 
marked by a rather abrupt slope called the " Fall Line," 
and in most places the line where they meet is quite distinct. 



60 PHYSICAL GEOGRAPHY 

Most of the rivers are navigable to the Fall Line, and along 
the eastern side coast a line of cities marks the junction. 

Almost every body of land is surrounded by a coast 
plain ; indeed its formation and' growth necessarily follows 
the denudation or wasting of the land. Rock waste is con- 
stantly being carried to sea-level by running waters, but 
beyond this point it can go little or no farther ; so it is 
distributed along the shore and levelled off by the waves. 
In most instances slow, vertical movements of the rock en- 
velope are concerned in the formation and development of 
coast plains, but in many cases rivers, waves, and tidal cur- 
rents divide the work among themselves. 

In various places surfaces formerly rugged have been 
levelled off by the action of the sheet of ice that once cov- 
ered portions of Europe and North America. Much of the 
northern part of the United States received the configura- 
tion of its surface by this process ; the moving sheet of 
ice scoured off the rugged parts and filled the depressions 
with the material removed. 5 

Distribution of Plains. — Alluvial and lacustrine plains, 
of course, are incidents in the physiography of rivers and 
lakes ; and coast plains are formed on nearly all shores. 
The great marine plains of the world are mainly on the 
slopes of the Arctic and the Atlantic Ocean. The most 
extensive plain of the world is that which forms the 
northern slope of Eurasia. From east to west it stretches 
a distance of about nine thousand miles ; from north to 
south, about three thousand miles. In Asia it is high and 
rolling ; in Europe the greater part of its extent, how- 
ever, is low and comparatively level. 6 

In the New World the great continental plain extends 
from the Arctic Ocean to the Gulf of Mexico, and there is 
an apparent extension from the Caribbean Sea southward 
through South America. Its continuity is broken by 



PLAINS, PLATEAUS, AND MOUNTAINS 61 

occasional ranges and arms of the sea. It presents cer- 
tain marked contrasts to the plain of the Asian Continent. 
The latter extends east and west ; the former, north and 
south. The latter is a margin of the continent ; the for- 
mer is an interior plain, bordered by mountain-ranges. 

Physiographic Aspect of Plains. — Although water is 
the chief agent in the formation of plains, it is likewise the 
chief factor in their destruction. From the moment a plain 
comes into existence, storm waters and running streams be- 
gin to carve channels in its surface. These, extending in 
area, carry the greater part — perhaps all the surface mate- 
rial away. 7 A plain thus channelled is said to be " dissect- 
ed." The coast plain of much of the South Atlantic and 
Gulf coast is young, especially near the sea. Its slope is 
so gentle that the streams have not yet carved their chan- 
nels to any great depth. 

The plains bordering Lakes Erie and Ontario show signs 
of greater age. The streams have accomplished a consid- 
erable dissection and the channels are comparatively deep. 
The " Bad Lands " of South Dakota and Nebraska are 
remnants of an old lacustrine plain that has been so greatly 
dissected that the region is well-nigh impassable through- 
out much of its extent. 

Economic Value of Plains. — Because of their com- 
paratively level surface, plains are more accessible to 
commerce than mountainous regions. Railways can be 
built across them at the minimum of cost, and the rivers 
that traverse them are usually navigable. 

More than this, the soil of plains is usually deep and 
easily cultivated. Therefore the}- are capable of support- 
ing a denser population than mountainous regions. In 
remote times the alluvial plains of the Nile and of Meso- 
potamia were the seats of dense population and vast in- 
dustries. In later times the plains of Europe and of the 



G2 PHYSICAL GEOGKAPHY 

United States Lave become the great producers of wealth. 
It may be said, therefore, that the greater part of the world's 
wealth and power is centred in the plains of the temperate 
zones. Only a small fraction of the world's population lives 
above the altitude of 2,000 feet, and but few of the great 
cities are more than six hundred feet above sea-level. 

Plateaus. — Almost any broad extent of country having 
an elevation of more than a few hundred feet, and an ir- 
regular or dissected 8 surface, is popularly called a plateau. 
The name, originally meaning " flat," or " level," has ac- 
quired a signification almost the opposite. A plateau of 
small area is usually called a mesa, a table-land, or a table- 
mountain, according to its general form and structure. 

Like most other elevations of the earth's surface, pla- 
teaus are the result of a gradual uplift of parts of the rock 
envelope. Most of the great plateaus of the earth are 
rimmed by lofty mountain-ranges, and their surfaces are 
generally traversed by ridges and valleys. Thus, the pla- 
teau region of western North America, nearly a mile and 
a half high, is bordered by the lofty ranges of the Kocky 
Mountains, and Sierra Nevada systems ; the great Boliv- 
ian plateau is margined by the highest summits of the 
Andes ; and the loftiest plateau in the world, that of Tibet, 
is enclosed by some of the loftiest ranges of the earth. 

Mesas and table-lands are generally the result of ero- 
sion, or unequal weathering. The top of the mesa is com- 
monly a layer of rock resting upon softer substance. The 
latter is protected from the action of the elements by the 
harder material and, in time a table-land is formed. With- 
out the hard cap the surface would have been rounded off, 
leaving a hill instead of a mesa. As a rule, mesas and 
table-lands are the outlying or isolated remnants of pla- 
teaus. They are noticeable objects because of their flat tops 
and the steep cliffs or escarpments that form their slopes. 





n 




H 








C 




2 




> 




n 




- 




o 




(n 




m 




H 




X 




m 




~n 


< 


r 
> 


- 


H 


5: 


> 


r 


C 






H 


> 




X 


— 


o 


— i 


*T1 


— 


o 



t/i 


,- 


> 


_ 


A 


T' 


o 


« 


■n 


O 


— 




> 


H 


H 


I 


m 


CD 


> 




r 


O 




> 




7!l 


2: 




O 


■?; 


73 




H 


O 


X 


"fl 


m 




> 


H 


i/i 


... 


H 


m 


1 


n 


^ 


O 
O 



Canon of Colorado River 



Hurricane Ledge 



Kanab Plateau 



Canon of Kanab River 



1 Mm 



Kaibab Plateau 



I 



Marble Canon 



Echo Cliffs 



■i \ M mm 

I Mi lliil 



64 PHYSICAL GEOGRAPHY 

Distribution of Plateaus. — Most of the high plateaus 
are in the great highlands that radiate from north circum- 
polar regions ; they face the Pacific and Indian Oceans. 
A series of lesser highlands borders the Atlantic Ocean, 
and these also contain plateaus. Although the plateaus 
have each a more or less definite outline they cannot al- 
ways be considered apart from the highlands to which 
they belong. In places where the highlands border the 
sea, the plateaus may take the form of peninsulas ; name 
several examples on the map of Asia. 

Among the plateaus of the Asian Continent, that of 
Tibet is remarkable for its size and elevated surface, near- 




A DISSECTED PLATEAU, JOHN DAY VALLEY, OREGON 
The sheet of lava at the surface has been removed here and there, leaving a scries of mesas. 

ly three miles above sea-level ; by what ranges is it partly 
enclosed ? To the westward are the Pamirs, a series of 
grassy plateaus, like the "parks " of Colorado, about three 
and a half miles above the sea. In North America, the 
plateaus of the western highlands are a little more than a 
mile high, while those of the eastern highland have less 
than half that altitude. In South America the plateaus of 
the Andes are about two miles high, while those of the 
eastern region have less than one-third that height. 

Economic Aspect of Plateaus. — Plateaus, especially 
those of a considerable altitude, are generally unproduc- 
tive. In some instances they are so high that but little 
rain falls ; in others the mountain rims shut off the moist- 
ure that is borne with the winds. The rugged slopes and 
deep canons almost always make commercial intercourse 



PLAINS, PLATEAUS, AND MOUNTAINS 65 

very difficult, and sometimes impossible, except to the 
rudest methods of communication. Because of their un- 
productive character the high plateaus, as a rule, are 
sparsely peopled ; and because of the lack of intercommu- 
nication the civilization of the native peoples is not usu- 
ally of the highest type. 

In the lower plateaus the conditions are different ; 
there is generally a rainfall sufficient for the production of 
food-stuffs, and the laud that cannot be cultivated is often 
well adapted to grazing ; meat, cattle products and wool 
are almost always associated with these plateaus. The 
broken aftd dissected rock strata in many instances yield 
minerals and metallic ores useful in the arts and sciences, 
and the rugged character of the surface often furnishes an 
abundance of water-power. In the New England Plateau 
of the United States one may see the results of surface 
conditions in the production of water-power ; in the Ap- 
palachian Plateaus, the results of coal and iron produc- 
tion ; and in the Iberian Plateau and Australia the re- 
sults of grazing facilities. The wool from these regions is 
the finest in the world. 

Mountains. — Mountains are the most characteristic 
and remarkable features of the landscape. In form, they 




A SECTION ACROSS THE UINTA MOUNTAINS 
tA single fold with fault. > After Powell. 

are great ridges marked by a very rugged surface. Iu 
structure, they are folds or wrinkles in the strata of the 
rock envelope, or else they are immense blocks of rock, 
broken and partly upturned. 



66 



PHYSICAL GEOGRAPHY 



Mountains occur usually in systems, eacli of which con- 
sists of many ranges, together forming a distinct group. 
A very extensive system is sometimes called a cordillera. 
Thus, the Rocky and Andean Systems from the great 
Cordillera of the Western Continent Ranges or folds that 
seem to be continuations, one of the other, are said to be 
a chain, as the Sierra Nevada and Cascade Mountains. A 
single fold may be worn away so that the broken strata 
form ridges ; or the crest may be weathered so unevenly 
that it presents the appearance of a series of notches, 
thereby forming a sierra. Any part of the crest or summit 

materially higher 
than the rest 
forms a peak. 10 
In most instances 
the peak is a high 
crag, or a pinna- 
cle, but the name 
is also applied to 
volcanic cones, 
and to elevations 
that more prop- 
erly are plateaus — as Broad Mountain, Pocono Moun- 
tain, and Broad Top, in the Appalachian system. 

A mountain system is characterized generally by great 
extent, several of the more important exceeding four or five 
thousand miles in length. Name three of the greatest 
systems. A range, on the contrary, rarely exceeds a few 
hundred miles in length. It gradually takes form, contin- 
ues a short distance, and then disappears, another to the 
right or the left taking its place. The rolling hills that in 
many instances form the approach to a system, are called 
foot-hills or, better, Piedmont lands. The hollow or de- 
pression between adjacent ranges forms an intermontane 




THE JURA MOUNTAINS 
<A series of gentle folds. 



PLAINS, PLATEAUS, AND MOUNTAINS 67 

valley ; or if wide and apparently enclosed, a park. A 
valley that extends across the range is called a j^ss, a gap, 
or a canon. 

Nature of Mountain Ranges. — In the simplest form, 
as the Uinta Mountains, there is a single fold ; in the Jura 



SECTION OF A DISSECTED RANGE 
c4 single fold is dissected into a number of ridges. 

Mountains there are several ; in other instances, as the 
Alps, there has been a mashing and crumpling of the 
strata, producing results as irregular and complex as though 
the leaves of a book had been pressed and crumpled side- 
ways by a great force. 

The folding process takes place slowly — so slowly, in 
fact, that no means exist whereby it can be measured ex- 
cept after long intervals of time. This is shown by the 
conduct of certain rivers that flow across the folds. The 
streams cut their channels downward quite as fast as the 
folds are pushed upward. So when the fold has become a 
lofty range, it is severed transversely by the stream. Had 
not the upthrust of the fold proceeded more slowly than the 
downward cutting of the stream, the latter would be 
turned aside ; in places this seems to have occurred, but 
even in such cases there is always evidence that the uplift 
of the range is very slow. 



68 



PHYSICAL GEOGRAPHY 



Excepting the core of granite, or similar rock that is 
present in the lower part, of many folds, monntain-ranges 
are composed of strata of sedimentary rock. Moreover, it 
is a notable fact that the strata which form them are mnch 
thicker along the folds than elsewhere. 11 Thus in the 
Appalachian Mountains, the sediments composing the 
folds are about 40,000 feet thick, while the same strata 
in the Mississippi Valley are scarcely more than 4,000 
feet in thickness. 

Not all ranges present the aspects of folds, however. 
The ridges in the Great Basin of the United States are 
great blocks of sedimentary rocks that have been broken 
and tilted, and left with edges partly upturned. The 
Sierra Nevada and Cascade Ranges are both folded and 
broken, and their abrupt eastern slope is the edge of an 
immense block tilted toward the Pacific. 




BLOCK MOUNTAINS, BASIN REGION 
The upturned edges form the ranges. 

The ideal system with its parallel folds exists, it is true, 
but it is not common. In most instances one finds a con- 
fused tangle of ridges and ranges, separated by intermon- 
tane valleys and crossed by gaps and passes. In not a few 
instances parallel ranges are connected by spurs, as in the 



PLAINS, PLATEAUS, AND MOUNTAINS 69 

Sierra Nevada and Coast Pianges ; and not infrequently 
several ranges seem to radiate from a massive uplift, as in 
the case of the Pamir highland, from which radiate the 
great folds that form the Himalaya, Tian Shan, Hindu 
Kush, and Suliman Mountains. 

Physiographic Aspect of Mountains. — From the mo- 
ment the process of uplift begins the waters of the atmos- 
phere begin to level off the folds. In general, the more 
prominent a topographic feature, the more exposed will it 
be to the factors that produce erosion. And although 
nearly every part of the rock envelope is undergoing denu- 
dation, uplifted surfaces generally suffer most. As the 
process of elevation goes on, the mountain torrents carve 
the slopes of the range into a multitude of valleys, canons, 
ridges, and hogbacks. 

Not only are the flanks sculptured, but the crests are 
also Avorn away. The tops of the folds being considerably 
broken and, at the same time, the most exposed, little by 
little are removed, leaving the upturned edges in the form 
of long ridges. Most of the ranges of the Appalachian 
Mountains are ridges formed in this manner; there are 
few folds, but many ridges. 

The amount of material removed from the slopes and 
crests of mountains is enormous. The crests of the Ap- 
palachian folds in Pennsjlvania are scarcely more than 
two thousand feet high at the present time ; but if all the 
material that has been removed could be again heaped 
upon them, their summits would be not far from ten miles 
high — about twice as high as the loftiest summits of the 
Himalayan folds. Usually the slopes and foot-hills are 
covered deep with coarse rock waste. 12 

Much — probably most — of this material has been re- 
moved by running water, but the moving ice sheet that at 
one time covered the northern part of the Appalachian 



70 PHYSICAL GEOGRAPHY 

highlands was also a powerful agent in sculpturing their 
crests and slopes. Thus, in the North Atlantic States and 
New York, where they received the full force of glacial ice, 
the highlands, in places, are worn down almost to the sea- 
level. In Pennsylvania, where the wasting was less ef- 
fective, they are about two thousand feet high. But in 
the South Atlantic States, beyond the limits of glacial 
ice, the various ridges are more than four thousand feet in 
altitude. 

As a rule, therefore, mountain-ranges which show but few 
effects of weathering are comparatively young. The tilted 
blocks of strata that constitute the short ranges of eastern 
Oregon as yet are scarcely notched by streams, and are 
very slightly weathered. The ridges of Nevada are much 
more worn and carved, and the Rocky Mountains, though 
young as compared with the Appalachian folds, are very 
much worn. The Laurentian folds, the oldest in North 
America, are worn so greatly that their highest crests are 
only a few hundred feet above sea-level. 

The character of the weathering and the landscape 
scenery as well depend partly on the rock and partly on 
the conditions of climate. In the Appalachian ranges all 
the forms are rounded, subdued, and graceful. In arid 
regions they are apt to be angular. The notched crests of 
western ranges of the United States and Mexico have sug- 
gested the name " sierra " (saw), the sharp, enduring crags 
of the Alps, " aiguille" (needle), " horn," and " dent " (tooth). 

Distribution of Mountains. — Mountain-ranges seem to 
be incidental to highland regions. The great highlands 
that border the Pacific and Indian Oceans are rimmed 
throughout much of their extent by very lofty folds. In 
North America the Rocky and Sierra Nevada ranges are 
the rims of a high plateau whose surface is traversed by 
block ranges. 



PLAINS, PLATEAUS, AND MOUNTAINS 71 

How is this statement borne out in the case of South 
America ? of Australia ? of Africa ? It does not seem ap- 
parent, however, in the case of Eurasia. The great system 
of southern Europe, extending from the Caspian Sea to the 
Atlantic, belongs to the principal highland of Eurasia. 
The Alps form the northern, and the Atlas Ranges of 
Africa the southern rim. What sea fills the intermon- 
tane valley between them? A partly submerged chain 
extends along the east coast of Asia ; name the penin- 
sulas and principal island groups belonging to it. In 
general the great systems are nearest the Pacific and Ind- 
ian Oceans. 

Valleys. — The folding of strata into parallel ranges 
naturally forms valleys between them. The great inter- 
montane valley of California, Oregon, and Washington is 
of this character. Name the ranges between which it is 
situated. Although interrupted by cross ranges it prac- 
tically extends from Puget Sound to the Gulf of Califor- 
nia. The valley, a part of which the St. Lawrence River 
now occupies, is similar in structure. 

Most valleys, however, are the results of stream-cutting 
and the general weathering that comes from the action of 
water. Shenandoah Valley, the depression crossing Vir- 
ginia, is an example. The rocks along the line of the val- 
ley were more easily worn away than those to the east 
and the west, and hence the valley resulted from their re- 
moval. The valley of the lower Hudson was possibly 
formed in a similar manner. 15 

In many instances the water wears away the broken 
rocks forming the crest of a range more easily than it can 
remove them elsewhere. In this way canoe-shaped valleys 
are formed at the summit of a fold. More commonly, 
however, the streams on opposite sides of a range wear 
their channels clear to the crest, partly breaking the lat- 



72 



PHYSICAL GEOGRAPHY 



ter down by making deep notches across it. Many of the 
passes in the Sierra Nevada and Rocky Mountains are ex- 
amples; 16 and so, too, are the water-gaps of the Delaware, 
Susquehanna, and Hudson Rivers. Water-gaps are usually 
at the base level of the range ; passes are usually high 
above it. 




CANOE VALLEYS, APPALACHIAN MOUNTAINS 

In a few instances the cross spurs that join parallel 
ranges enclose valleys of considerable extent. The Parks 
of Colorado, and the Pamirs, both frequently classed 
among plateaus, are examples. The latter are situated in 
a high mountain knot which, because of its great height, 
is often called the " Roof of the "World." 

Economic Aspect of Mountains. — Notwithstanding 
the fact that mountains are sparsely settled, and include a 
very large proportion of uncultivable land, they neverthe- 
less exert a great influence on life, its history, and its in- 
dustries. Ranges that face rain-bearing winds may be so 
lofty that they intercept all the moisture. How do the 
Cascade and Sierra Nevada ranges illustrate this ? How 
does this affect the habitability of the region west of their 
summits ? In various localities ranges at a considerable 
distance from the sea chill the winds passing over them 
and condense the moisture that otherwise would not be 
precipitated. Mountains, therefore, are factors in the dis- 
tribution of rain. 



PLAINS, PLATEAUS, AND MOUNTAINS 73 

The broken folds of the strata frequently expose metals 
and minerals that otherwise would not be accessible. Al- 
most all the gold and silver, the mechanism of exchange, 
come from mountain-ranges ; and so, also, does most of 
the copper, a metal necessary in the transmission of elec- 
tric power. Practically all the anthracite coal and much 
of the best iron ores are associated with the rocks of 
mountain-ranges. The latter are, therefore, essential to 
the industries of mankind. 

Mountains affect life and its industries mainly because 
they are barriers to intercommunication. The Greek peo- 
ples of early times found it much easier to spread along 
the shores of the Mediterranean and across the iEgean 
Sea than to cross the Balkan Mountains. For the first 
fifty years of our national history there was no transcon- 
tinental intercourse between the Atlantic and Pacific 
coasts of our country. It was easier to go sixteen thou- 
sand miles around Cape Horn than to traverse one thou- 
sand miles of mountainous surface. 

The effects of intercommunication may be seen in the 
case of the Basques. More than two thousand years ago 
the} T were driven from the lowlands of Spain and France 
into the almost inaccessible valleys of the Pyrenees Moun- 
tains. During the succeeding years they have been so little 
in contact with the rest of the world that their language 
and customs have been changed but little in that time. 

Because of the differences of climate on opposite sides 
of high ranges, the distribution of life-forms is greatly re- 
stricted. The dense forests of the Pacific Coast can- 
not extend across the Cascade and Sierra Nevada Ranges, 
because there is not enough moisture to support them. 
On the other hand, not many of the plants of the arid side 
of the mountains can cross the ranges and survive because 
the conditions of climate and soil are unsuitable. 



PLAINS, PLATEAUS, AND MOUNTAINS ?5 

Intermontane valleys are usually productive, and there- 
fore densely peopled, areas. As a rule, their fertility can- 
not be easily impaired, because fresh soil is brought to 
them with every flood season. Because of the infertile 
region on either side, the industries of life are of neces- 
sity concentrated in the valleys. 

Passes have even greater importance than valleys. A 
mountain-range is an obstacle to communication, and the 
pass is, therefore, the channel toward which intercourse 
must be concentrated. Railway routes through mountain- 
ous regions are always surveyed and built through the 
passes. Almost every railway to the various commercial 
centres of the Atlantic seaboard seeks a way through the 
passes and water-gaps of the Appalachian Mountains. 

To Mohawk Gap, a pass that practically forms the 
principal route of traffic between the Great Lakes and 
the Hudson River, the wonderful development of New 
York City is due. It is more nearly level thau any other 
route across the Appalachian Mountains, and for this rea- 
son it furnishes a standard by which freight rates between 
Atlantic seaports and the Mississippi basin are regulated. 

Khyber Pass, a narrow defile a few miles east of Kabul, 
for more than two thousand years has been a part of one 
of the great overland routes between Europe and India. 
Indeed, it is the chief gateway to India ; and the truth of 
the old saying, " whoso would be master of India must 
first make himself Lord of Kabul," is every day more and 
more emphasized. It is evident, therefore, that inasmuch 
as mountains are a barrier between peoples upon their op- 
posite sides, all the intercourse and communication must 
be concentrated at the passes. 

QUESTIONS AND EXERCISES. -Name and classify the vertical 
forms in the State in which you live. On an outline map, shade or oth- 
erwise designate the areas of highland and lowland, using such contours, 



76 PHYSICAL GEOGRAPHY 

or lines of equal altitude, as may be available. If possible use the Re- 
lief Map of the United States noted below. 

Make a relief model in sand or paper pulp of any locality, the topog- 
raphy of which you know — State, county, township, or other region 
of interest. 

What results might occur were a mountain fold to be formed across 
the channel of a river ? 

Make a sketch restoring the plateau or mesa dissected by weathering 
processes, as shown on p. 64. 

Name some of the benefits and the disadvantages resulting from the 
presence of the Appalachian Mountains between the industrial centres 
of the Atlantic Coast and the Mississippi Valley. 

Explain why Fort Ticonderoga and Crown Point were important 
localities during the colonial wars. {Consult any good map of Lake 
Champlain.) 

On an outline map of each continent, or grand division, draw heavy 
lines representing the positions of the principal mountain-ranges. 

In what general direction does the rock waste of mountains move ? — 
Explain why. 

Give reasons why lowlands are more densely peopled than high- 
lands. 

COLLATERAL READING AND REFERENCE 

McGrBB. — The Piedmont Plateau. National Geographic Mag- 
azine, vii, 261. 

Willis. — Physiography of the United States, pp. 169-202. 

Hayes. — Physiography of the United States, pp. 305-336. 

Powell. — Exploration of Grand Cafion, pp. 181-193. 

United States Geological Survey Maps, the following 
sheets : Tooele, Marion, Sierraville, Marysville, Kaibab, Farmer- 
ville, Spottsylvania, Mount Monadnock, Mount Mitchell, Hurn- 
melstown, and others. 

NOTES 

1 The difference in the surface features of these plains is due 
partly to altitude and partly to rainfall. The Pampas resemble 
the high plains east of the Rocky Mountains. Both slope from a 
high to a low level, and both are covered with ' ' bunch-grass " — 
that of the Pampas being a very coarse species that grows to a 



PLAINS, PLATEAUS, AND MOUNTAINS 7? 

height of four or five feet. The Llanos .are watered by periodical 
rains and are alternately a swamp and a sun-baked desert. The 
Silvas lie in a region of almost constant equatorial rains ; hence 
they are adapted to tropical forestry . The Pampas and Llanos 
produce Avild cattle and horses ; the Silvas, rubber and ornamental 
woods. 

2 It will be swept by simoon winds because it will be practically 
a desert, for it is in such regions only that simoon winds are 
found. The same is true of the valley of Great Salt Lake : it 
will be a desert region as soon as the lake disappears. 

"Alluvial plains are the most productive lands in the world. 
Because their soil is constantly replenished by overflows and 
freshets they rarely wear out ; the nutrient elements are sup- 
plied about as fast as they are exhausted. 

4 The Atlantic Coast Plain varies from a few miles to more than 
one hundred in width. The more recently formed parts are cov- 
ered with pines ; and a broken, narrow belt of pine forest extends 
from Chesapeake Bay almost to the Rio Grande. To the east- 
ward of the pine barrens is a belt of sand flats and swamps of still 
more recent origin. 

6 Diluvial plains in places are strewn with large bowlders and 
covered with a " drift " composed of sand, unsorted gravel, clay, 
and bowlders. 

6 A similar plain involves the northern part of North America. 
In the New World, however, it loses many of the topographic 
features of a plain and is, perhaps more accurately, a low, but 
rugged plateau. Its slope, however, like that of the Eurasian 
plain, is toward the Arctic Ocean, and like the latter plain, its 
coastal portion is bordered by tundras. Generally considered, 
this plain is a vast basin almost shutting the Arctic Ocean from 
the rest of the sea. 

1 Plains are quite as subject to the same weathering processes 
as are mountains and plateaus, but because of their gentler 
slopes, the rate of erosion is not so great as in mountainous 
regions. The bluff lands along the Mississippi and some of its 
tributaries are thus dissected. Their complete degradation is a 
matter of time only. The higher parts of the Atlantic Coast 
Plain have been also greatly dissected by streams. In many in- 
stances the stream valleys and Hood plains cover an area equal 
to the inter-stream uplands. In strong contrast are the low, 



78 PHYSICAL GEOGRAPHY 

recently formed marine plains along the southern coast of New 
Jersey, and the still younger tule plains of the Sacramento 
Valley. In these the rivers have hardly been able to select their 
channels, much less to extend them. 

8 A high plateau sparsely covered with vegetation is much more 
readily dissected by streams than a grass-covered surface. The 
region through which the middle course of the Colorado River 
flows is an example. Here the plateau has been cut to a depth 
ranging from three thousand to six thousand feet. The region is 
one of deficient rainfall, however. Extensive corrasion is shown 
along the beds of the streams that rise at a distance in snow- 
clad mountains. Only a small part of the plateau as yet has 
been removed, and large areas show but little signs of dissec- 
tion. In other parts, however, such as the "Land of Standing 
Rocks," denudation has been enormous, and only the towers of 
harder rocks remain. A complex dissection may be seen in vari- 
ous parts of the Appalachian highlands. Here, because of a 
greater rainfall, the streams have formed a network of canons 
throughout the regions. 

9 Such formations are very common in the lava-covered regions 
of the Sierra Nevada and Cascade Mountains ; they are also found 
in the Piedmont lands of western Texas. 

10 There are many examples of isolated peaks, or ' ' monad- 
nocks, " in those mountain-ranges that have been very greatly 
worn. Mount Holyoke is one of several examples in Massachu- 
setts. It was not thrown up in its pi*esent form ; on the con- 
trary, it was left when the rest of the range, being softer, was 
worn away. Mount Monadnock, New Hampshire, is a similar 
example. Isolated ridges or ranges are more common, and ex- 
cellent examples may be found in the Great Basin. 

11 Not only were the deposits that became sedimentary rock 
thicker before the folding took place, but they were made still 
thicker by side pressure and crumpling. 

12 At the mouth of every canon there will be found a fan-shaped 
pile of coarser material called talus. A pile of talus is usually 
found at the bottom of every steep, rocky cliff. 

13 A large part of Rhode Island and Connecticut constitutes the 
base of an old mountain highland that has been worn down al- 
most to sea-level. 

14 Both valleys have been modified by water, the depression 



PLAINS, PLATEAUS, AND MOUNTAINS 79 

having been submerged, partly filled with sediment, and re-ele- 
vated. 

15 It is not unlikely that the process has been more complex, 
and that periods of elevation have alternated with those of rest. 
Old shorelines and deposits of river gravel occur all along the 
lower river. The numerous clay banks seem also to have been 
deposited by slack water. The lower part of this valley is now 
practically an estuary. 

16 Among the famous passes are Argentine, 13,100 feet, the 
highest wagon road pass in the world ; Marshall Pass, 10,900 
feet, one of the highest railway passes in the world ; Alpine Pass, 
13,550 feet, and Mosquito Pass, 13,700 feet — all in Colorado. Sirn- 
plon, St. Bernard, and Brenner are famous passes across the Alps, 
and for centuries they have been highways of commerce. A rail- 
way pass across the Andes is nearly 14,000 feet above sea-level. 

In many instances the pass is not fully surmounted ; instead 
of building the railway over the divide, it is more economical to 
construct a tunnel under it. Some of these tunnels are marvels 
of engineering skill. St. Gotthard and Mont Cenis tunnels 
through the Alps ; Hoosac tunnel through the range of the same 
name in Massachusetts ; San Fernando tunnel, in California ; 
and the tunnel of the Transandine Railway are examples : each 
is one mile or more in length. In other cases the railway sur- 
mounts the range by a series of long and intricate loops, crossing 
and recrossing itself through tunnels that often are sharply 
curved. Near Caliente, California, the Southern Pacific Rail- 
way is built in sinuous loops aggregating about twenty miles in 
order to cross a divide scarcely two miles from the head of the 
valley. The famous loops of the Colorado Midland over Hager- 
mans Pass is also a well-known example of the railway builders' 
skill. 



CHAPTER V 

DESTRUCTIVE MOVEMENTS OF THE BOOK ENVELOPE : 
VOLCANOES AND THEIR PHENOMENA 

Or the various phenomena that attend changes in the 
level of the rock envelope, two of them, volcanoes and 
earthquakes, are noteworthy because the results are more 




VESUVIUS, A TYPICAL CINDER CONE 
From a model. — tAfter UH^asmyth. 



or less destructive. In the one case, great quantities of 
molten matter are ejected from fissures or vents, covering 
very large areas ; in the other, there is a movement at 

80 



VOLCANOES AND THEIR PHENOMENA 81 

some part or other of the rock envelope, so sudden that a 
tremor, or even a severe shock, occurs. 

Volcanoes. — A channel or vent in the rock envelope 
from which great quantities of steam arid molten rock are 
ejected constitutes a volcano. 1 In most instances a great 
deal of material, in the form of clots of half-molten rock, 
fall about the vent and build up a conical pile, sometimes 
called a "volcano," but more properly, a cinder cone. At 
the top of the latter is a cup-shaped depression called the 
crater or, if very large, the caldera.' 4 

Volcanoes showing any display of energy are said to be 
active, quiescent, or inactive, according to the character of 
their energy ; those in which all signs of activity seem to 
have disappeared are said to be extinct. 3 In a few in- 
stances the activity seems to be continuous. Thus the 
caldera of Maun a Loa nearly always contains lava in its 
molten condition, and Stromboli, " the Lighthouse of the 
Mediterranean," has been a mariner's beacon for more 
than two thousand years. Most active volcanoes, how- 
ever, are intermittent in action, alternating their eruptions 
with long periods of rest. 

Phenomena of Eruption. — In certain respects all vol- 
canic outbursts are similar ; that is, lava and steam are 
ejected from a subterranean source, and the matter ejected 
is forced out of a vent or channel in the rock envelope. 
Beyond this, however, the various types of eruption have 
but little in common. In most cases the eruptions are 
very destructive. Frequently they are preceded by earth- 
quakes, though these warnings are by no means always 
present. Generally they begin with explosions that rend 
the top of the cinder cone in fragments. In some instances 
the plug of hardened lava that filled the channel is blown 
out, but quite likely a new channel is formed at the one 
side or the other. 4 



82 



PHYSICAL GEOGRAPHY 



A vent once made, the water tbat had accumulated about 
the cinder cone, together with mud and fragments of rock, 
are hurled upward ; an outrush of steam mingled with 
mud and rock waste follows, and a cloud of inky blackness 
quickly envelopes the cone. The condensing steam, with 
which sulphureous vapors are sometimes mingled, produces 
heavy rains ; and if sulphur gases are present, the rain 
may become so corrosive that vegetation is blighted and 
in many instances the crops are destroyed. 5 

A flow of lava follows. At first the lava is ejected with 
almost explosive violence, but after awhile the flow be- 
comes steady and 
regular. 6 The 
ejection of mate- 
rial takes place, 
not only at the 
main vent, but at 
the score of new 

IDEAL SECTION OF A VOLCANO OUeS tomied OU 

EMinor eruptions are taking place through fissures in the flanks the flanks OI the 
of the cinder cone, building parasitic cones. _ 

old. At each vent 
small monticules, or 'parasitic cones, are quickly formed, 
and the eruption from them does not differ materially from 
that at the main vent. 

Volcanoes such as Stromboli display but comparatively 
little explosive energy. From an overhanging crag of 
this volcano the eruption may be safely studied. At inter- 
vals of fifteen or twenty minutes a gigantic bubble begins 
to form in the caldron of seething lava. In <c few mo- 
ments it rises to the top and bursting, hurls a shower of 
lava clots into the air. 7 The eruptions of the Hawaiian 
volcanoes are materially different from those of the Strom- 
bolian or the Vesuvian type. Instead of the intermittent 
bubbles of Stromboli, or the violent outburst of Vesuvius, 




VOLCANOES AND THEIR PHENOMENA 83 




the lava rises in the caldera until it overflows the lowest 
part of the rim. 8 The flow of lava — often an enormous 
quantity — continues for several days, or perhaps for sev- 
eral weeks, and then subsides as quietly as it began. 

The Assure eruptions that occurred in previous geologi- 
cal periods seem to have somewhat resembled those of the 
Hawaiian volcanoes. In these eruptions there were ap- 
parently none of the phenomena that mark outbursts of 
the Vesuvian type. Great fissures were formed, and 
through these 
the lava was 
forced. 9 In some 
instances there 
was an enormous 
flow of lava ; in 
others the lava 
merely filled the 
fissure and hard- A laccolite 

ened, leaving <A section through one of the Henry Mountains. The dotted 

lines indicate the strata removed by erosion. 

dykes 01 vol- 
canic rock. The plains of the Columbia are the rem- 
nants of a flood of lava from fissures in the Sierra Nevada 
mountains. The Palisades of the Hudson form a dyke 
of similar character. 

In a few instances a flow of lava, thrust upward, has 
raised the outer strata of the rock envelope in much the 
same manner that a blister of the skin is formed. No 
extrusion of lava took place, and, as a rule, none reached 
the surface. Irruptions of this kind form what are com- 
monly known as laccolites. The Henry Mountains, a de- 
tached group of knolls in Utah, are examples. 

Products of Eruption. — Excepting the very small 
amount of sulphur gases emitted, practically but two sub- 
stances are ejected from volcanoes — steam and lava. In 



84 PHYSICAL GEOGRAPHY 

the eruption of Vesuvius that occurred in 1872, it is esti- 
mated that ninety-eight per cent, of the material ejected 
consisted of steam. From the Hawaiian volcanoes, how- 
ever, the matter thrown out consists almost wholly of 
great quantities of lava. 

The term lava includes every form of molten rock of 
volcanic origin. Lavas, therefore, differ not only in ap- 
pearance, but in chemical composition as well. In many 
instances the lava resembles furnace slag, and has about 
the same composition. Sometimes it is vesicular, or 
spongy ; pumice-stone, or " volcanic froth," is so porous 
that it floats on water. Obsidian, or " volcanic glass," an- 
other form, does not differ materially from black bottle- 
glass. The sponge-like clots of lava that accumulate about 
volcanoes form scoria ; they are suggestive of furnace 
" clinkers." 

A misunderstanding of volcanic phenomena has led to 
the adoption of certain names that often give erroneous 
ideas of volcanic action. There are no " flames " about 
volcanic outbursts ; the so-called flames are merely the 
reflection of the white-hot lava from the under surface of 
the dense clouds of steam. 10 " Smoke " is also absent, 
except as the clouds of dust and steam can be thus 
called. Volcanic " ashes" are not ashes at all ; they con- 
sist merely of finely divided lava. It is thought that this 
form of lava results from the action of steam which, forced 
through the lava by intense pressure, carries much of it 
along in a fine, powdery state. 

Most lavas are readily decomposed by the action of air 
and moisture, and the Hawaiian lavas make excellent soil 
in the course of a very few years. The economic value of 
lavas, therefore, may be considerable. Sulphur, or " brim- 
stone," is a common mineral in and about the craters of 
volcanoes. It is formed by the action of certain sulphur 



VOLCANOES AND THEIR PHENOMENA 85 

gases that, on mixing, decompose each other and deposit 
the sulphur in the shape of crystals. 

Nature of Volcanoes. — That the cause of volcanic ac- 
tion is due indirectly to the gradual shrinkage of the crust 
of the earth is admitted by most geographers. To what 
extent the process of contraction becomes a direct cause, 
however, is a matter of uncertainty, and one upon which 
there is a great diversity of opinion. It is generally con- 
ceded, also, that the material ejected comes, not from an 
assumed " liquid interior " of the earth, but is formed 
at a very moderate depth below the seat of eruption. 




J^R. 



FORMS OF ERUPTION 



A, a dyke; B, E, subterranean intrusions; C, a cinder cone; D, a laccolite; F, a lava sheet; 
G, granite core of a range. 



Various theories have been advanced to account for the 
possible causes of eruption, but of these only one or two 
are supported by positive evidence. The pressure that 
results when the rock layers fit themselves about a shrink- 
ing interior is sufficient to heat the parts upon which the 
pressure is exerted, far beyond the temperature of fusion ; 
and if a break or fracture takes place, the pressure being 
relieved at that point, the superheated rock at once 
liquefies and is forced out of the fissure. The intrusion 
of water upon molten matter undoubtedly causes the ex- 
plosive features of the eruption, but it is improbable that 
this is the prime cause. 



86 PHYSICAL GEOGRAPHY 

In a few instances there seems to be more or less re- 
lation between volcanic vents situated at no great dis- 
tance from one another. Thus, while Vesuvius was so 
loug inactive, Epomeo on the island of Ischia was active ; 
but after the eruptions of Vesuvius began again, Epomeo 
became dormant. A similar condition possibly obtained 
in past times, for the Phlegrean Fields, an area south of 
Vesuvius, is honeycombed with old craters through which 
eruptions took place at successive intervals. 

The same phenomenon is observed in the case of the 
Hawaiian and the Ecuadorean groups. Activity is us- 
ually confined to a single caldera, and if this becomes 
dormant for any length of time the seat of activity is 
transferred to another vent. In the cases of the Italian 
and the Ecuadorean groups, the cessation of all activity is 
usually followed by a period of frequent and destructive 
earthquakes. 

Results of Vulcanism. — Notwithstanding their stu- 
pendous display of energy, the physiographic effects of 
volcanic outbursts are comparatively unimportant, and as 
a rule they are confined to the vicinity of the volcano. 
The most noticeable feature is the cone or dome that pop- 
ularly is called a volcano or volcanic peak. Each volcano 
builds its own cone, and in many instances the cones 
have been built along the folds of mountain-ranges. In 
several cases they have been formed successively along the 
line of the fold at no great distance apart. 

The lava usually collects at the vents, extending later- 
ally outward, and at the same time building the cone high- 
er and higher. The successive eruptions of the calderas 
of Hawaii have formed a mass 14,000 feet high that covers 
an area as large as the State of Connecticut. Most of the 
volcanic mountains of the Hawaiian Islands are dome- 
shaped rather than conical, the shape resulting from the 



VOLCANOES AND THEIR PHENOMENA 



87 



very liquid condition of the lava and the absence of ashes 
and scoria. 

Some of the lava flows of the Iceland volcanoes have 
been extensive. Of the thirteen or more cinder cones in 
the island Hekla and Skaptar Jokul are the best known 
because of the frequency of their eruptions. In 1783, 
there occurred a flow of lava from the latter that contin- 
ued for two years. Two streams flowed in nearly oppo- 
site directions from the crater, one forty, the other fifty 
miles in length. More than 1,000 square miles in area 
were covered by the lava. A score of villages was swept 
out of existence. Streams were dammed by the lava and 





A LAVA FLOOD, HAWAIIAN ISLANDS 



their floods added to the destruction. Thousands of cat- 
tle were killed, and a large part of the population perished 
in the famine that resulted from the eruption. 

The ashes sometimes accomplish more ruin than that 
which results from the lava flow and the corrosive rain. 



88 PHYSICAL GEOGRAPHY 

Herculaneum and Pompeii were destroyed by the erup- 
tion of Vesuvius a.d. 79. Pompeii was covered Avitli loose 
material, and much of the city has been excavated in re- 
cent years. Herculaneum received a heavy fall of rain 
m addition to the ashes, and the latter were cemented 
into a tolerably hard rock. 

In many instances the ashes have been hurled to a great 
distance, being in part carried by the wind. During the 
eruption of Tomboro, in Sunda Strait, dwellings forty 
miles distant were crushed and large areas of forestry were 
destroyed. Similar, but more appalling effects resulted 
from the eruption of Krakatoa, also in Sunda Strait. The 
explosions lasted for two days and culminated with the 
disappearance of half of the island. Forestry seventy-five 
miles away was crushed by the falling mud and rain, and 
the fine material covered the city of Batavia to a depth of 
several inches. Some of the lighter dust was carried by 
the wind to a distance of more than 1,000 miles. 

Islands are both formed and destroyed by the outbursts 
of marine volcanoes. Off the coast of Tunis, near the 
site of Carthage, a reef called Graham's Island was formed 
during an eruption, and remained in existence for several 
years. It then gradually settled below sea-level and dis- 
appeared. Several new islands appeared in the group of 
the Azores, during eruptions, but they gradually disap- 
peared. A more remarkable case is that of Santorini, 11 
an island in the Greek Archipelago, which was formed as a 
result of eruptions. It is iioav inhabited. 

Fissure eruptions are noted mainly for the enormous 
flows of lava. From one or more of these fissures in the 
Sierra Nevada ranges there occurred a flood of lava that 
covered more than one hundred thousand square miles. 
Large areas of California, Oregon, Washington and Idaho 
were engulfed, and in several places the Columbia River 



VOLCANOES AND THEIR PHENOMENA 89 

was pushed out of its channel. In many places small 
cinder cones have been formed on the surface of the 
lava, each being an eruption upon an eruption. In places, 
the sea of lava is nearly four thousand feet deep, and the 
average depth is not far from one thousand feet. 

Vulcanism seems to be a trustworthy index of processes 
going on within the earth's crust which affect the level of a 
region. Careful measurements have shown that, in regions 
of volcanic activity, an elevation of the surface is taking 
place. Thus, along much of the Mexican and South Amer- 
ican coast, where volcanic forces are active, upheaval is 
taking place. In the South Pacific Ocean, on the con- 
trary, where vulcanism seems to have recently ceased, 
there has been a considerable subsidence. It cannot be 
said with certainty, however, that these are matters of 
cause and effect. 

Distribution of Volcanoes. — Volcanoes are commonly 
found along the lines of the younger mountain folds, and 
they are almost always near the sea. The Pacific Ocean 
is nearly girdled by chains of mountains that are com- 
paratively young, and in these folds are situated a majority 
of the active and dormant volcanoes of the earth. 

Another short chain extends along Java and the re- 
maining Sunda Islands to New Zealand. It contains 
about one hundred active and dormant volcanoes, and is 
the chief seat of volcanic activity on the earth. The Ha- 
waiian group is about the only one situated in mid-ocean. 
In what direction does it extend ? This chain is about a 
thousand miles long. The seat of activity, however, is con- 
fined mainly to the island of Hawaii, on which there are 
three calderas — Kea, Loa, and Kilauea. 

A chain of volcanic islands extends from Jan Mayen 
island through Iceland, the Azores, Canary, and Cape 
Verd Islands, southward as far as Tristan da Cunha. An- 



90 PHYSICAL GEOGKAPHY 

other extends through the West Indies, but it contains no 
volcanoes at present active. Graham Land, in the Ant- 
arctic Continent, contains at least two volcanoes that 
have been active in recent times. 

Among American volcanoes the Peruvian and Ecuado- 
rean groups are famous for their great height. Name three 
of them. The Mexican group contains four of interest, 
because they are so far inland. Find them ; in what 
direction does the line extend? They are active or quies- 
cent at short intervals. 

The North American group contains a great many 
dormant and extinct cones ; but at least four — Shasta, Ta- 
coma (or Rainier), and Lassen must have been active at 
no greatly remote time. A small cone near Lassen Peak 
has been in eruption within fifty or sixty years, and the 
stumps of trees, many of them in a good state of preserva- 
tion, are still protruding through the sheet of lava. 

Cinder cones and volcanic " necks " are abundant all 
through the plateaus of the Western Highlands. In Ari- 
zona there are several hundred. One of the most imposing, 
San Francisco Peak, has been in eruption within recent 
times. In New Mexico there are also many small cones. 
Almost all the high peaks of the Cascade and Sierra Ne- 
vada ranges are cinder cones. 

The Aleutian group contains about thirty cones, quies- 
cent and active. One of these, Bogoslov, north of Una- 
laska, has been in eruption almost constantly since 1880. 
Many of the peaks of the West Indies are cinder cones, 
but none has been active in recent times. The remains of 
old cones are abundant in the Appalachian and Laurentian 
Mountains, but they seem to have been extinct since early 
geological times. One of them, Mount Royal, has given 
to the city of Montreal its name. 



VOLCANOES AND THEIR PHENOMENA 91 

QUESTIONS AND EXERCISES.— Explain the nature of the so- 
called smoke, flames, and ashes of volcanic eruptions. Why are these 
terms inapplicable ? 

Prepare a written description of the geographic distribution of vol- 
canoes, taking into consideration their position with reference to moun- 
tain-ranges, proximity to the sea, latitude, and situation with reference 
to continents and islands. Consult the map, p. 92. 

Note the features in the diagram, p. 88, and prepare a brief descrip- 
tion of the various ways in which lava is extruded. 



COLLATERAL READING AND REFERENCE 

Pliny.— Letters— Book vi., 16-vi. 20. 
Shaler. — Aspects of the Earth, pp. 46-97. 

First Book of Geology, pp. 88-97. 
Le Conte.— Elements of Geology, pp. 89-103. 
Redwat and Hinman. — Natural Advanced Geography, p. 12. 
United States Geological Survey. — Shasta and Lassen 
sheets. 

NOTES 

1 The channel or tube is the essential part of the volcano, and 
the " mountain " or cinder cone is merely an incidental feature. 
The latter is rarely absent. 

" The craters of the earth are exceedingly small, compared with 
those of the moon. Terrestrial craters are rarely more than half 
a mile in diameter ; lunar craters, on the conti - ary, frequently ex- 
ceed twenty or thirty miles in diameter ; Tycho and Copernicus, 
are each more than forty miles. 

3 As a rule, such volcanoes are rarely distinguishable, except by 
most careful investigation. Usually the cone has been almost 
obliterated, nothing remaining except such masses of lava as are 
not easily altered by the action of moisture and atmospheric ele- 
ments. Mount Tom, Massachusetts, is an excellent example 
of an old volcano. 

4 The eruption of Vesuvius in 1756 took place, not at the former 
crater, but a little to one side. One of the old crater walls re- 
mained standing, and for many years was called Monte Sunima. 
During the eruption of 1872 a large Dumber of vents was Formed, 



VOLCANOES AND THEIR PHENOMENA 93 




and the flanks of the mountain were clotted with monticules. 

Professor Palmieri, who remained in his observatory on the 

mountain during the 

entire period, said that 

the whole side of the 

eone "seemed to sweat 

fire at every pore." 

■ The sulphur com- 
pounds combine with 
the steam, making sul- 
phurous acids, and not 
infrequently the acid 
dissolved in the rain is 
strong enough to de- 
stroy vegetation. 

6 It behaves exactly 
as though it were forced 
out by gases under ex- 
tremely high pressure, 
the elasticity of the 
medium that consti- 
tutes the power being 
the most noticeable 
feature. 

7 The phenomena are 
simply those exhibited 

by a viscous body in a state of slow boiling, and are perfectly 
illustrated in the slow cooking of oatmeal. It is a significant 
fact that when the barometer is low, the level of the lava is 
higher than at other times. 

6 There is evidence of the presence of gases in the Hawaiian 
lavas, not under pressure and endeavoring to escape, but in a con- 
dition of absorption or occlusion. Occasionally, (dots of lava are 
shot [ntotheair, and as soon as the ejected muss percept i lily cools, 
its absorptive power is lessened, the escaping steam or other vapor 
blowing the viscous lava into the fine, tenuous threads known as 
"Pele's hair." The threads thus formed are so gossamer-like 
that they are carried a long distance by the wind. 

'There is a tendency to consider the vulcanism of past epochs 
as crater eruptions only. That such eruptions have occurred in 




ALTERATIONS IN THE SHAPE OF VESUVIUS 
<AfD. 6), 19 to i6ti, 7767, iS 22, 186S. 



94 PHYSICAL GEOGRAPHY 

prior epochs cannot be denied ; old craters and the lava plugs 
that filled them are found in great numbers in many parts of the 
earth. Most, if not all, of the great lava floods, however, came, 
not from craters, but from fissures. No crater in the world is large 
enough to have ejected a lava flood in the manner in which that 
of the Oregon and Washington flood was spread. Calderas like 
those of Hawaii would have built up a dome-shaped mass of 
ejecta. The lava flood in question was a sheet. It could have 
come from nothing but a fissure, and the fissure must have been 
many miles in length. Cinder cones and craters are found here 
and there on the surface of this vast sheet. In each case the cone 
and its crater represent a volcano that formed on the lava flood 
after the surface had hardened. This fact indicates that vulcan- 
ism occurs just as readily with a supramontane as a stib-moun- 
tain reservoir. In many instances there has been nothing more 
than a mere filling of the fissure — an intrusion of lava, but no ex- 
trusion. Not infrequently the upper edges of the fissure walls 
have been worn away, leaving the harder volcanic rock in the 
form of a ridge or dyke. The Palisades of the Hudson are an ex- 
ample. The Devil's Slide, in Weber Canon, Utah, is also an illus- 
tration. In this instance there are two dykes about twenty feet 
apart, the groove between them being of softer rock. 

10 This may be illustrated by a very familiar example. When 
a train of railway coaches passes through a long tunnel, a flood 
of mellow light now and then illuminates the tunnel and the in- 
terior of the coaches. The light comes from the fire-box of the 
locomotive. When the furnace door is opened the light of the 
glowing coal is reflected from the steam that fills the tunnel. 
Each globule of water dust is a tiny mirror, and as a result the 
tunnel is flooded with light. In the case of the volcanic " fires " 
the light is reflected from the under side of the cloud of steam. 

11 This island, better known as Thera, is a few miles north of 
Crete. According to one myth it grew from a clod of earth hurled 
from the ship Argo ; according to another it was the product of 
submarine fires. Both legends are a testimony to its volcanic 
origin. The topography of the island was considerably altered 
by an eruption that occurred in 1866. The area covered by ashes 
and scoria quickly became cultivable, and has since added no lit- 
tle wealth to the island. 



CHAPTER VI 

DESTRUCTIVE MOVEMENTS OF THE ROOK ENVELOPE : 
EARTHQUAKES 

Rigid and solid as they seem, the substances that form 
the rock envelope are more or less elastic. This is notice- 
able when an underground explosion ! occurs, or eveu when 
a very heavy weight falls to the ground ; the latter trem- 
bles for an instant, causing a slight shock. 

Any instantaneous disturbance, therefore, such as a sub- 
terranean explosion, the collapse of a cavernous space, or 




THE PROGRESSION OF EARTHQUAKE WAVES 

the sudden breaking of strata, causes a vibration or trem- 
bling of the surrounding rock. These tremors or earth- 
quakes may be perceptible for several seconds, or even 
for so long as a minute. The shock, moreover, may in- 
volve an area of several thousand square miles. 

Nature of Earthquakes. — No matter how far below 

95 



96 PHYSICAL GEOGEAPHY 

the surface of the rock envelope the centre of the disturb- 
ance may be, as soon as the vibrations reach the surface 
they behave just as do the circular waves that form when 
a stone is thrown into still water. 2 In the diagram on 
page 95 the shock originates at O ; at what place will the 
resulting Avave have an up-and-down motion ? These are 
called vertical waves. As the successive waves move out- 
ward, little by little the vertical movement gives place to 
one that is both horizontal and progressive, and the latter 
may be called a horizontally progressive wave. At what 
part of the diagram are the waves most nearly horizontal ? 
Where do they partake both of the vertical and the pro- 
gressive character ? 3 

The effects that have been observed, however, indicate 
that the tremors or vibrations do not always spread out so 
evenly from the centre of disturbance as is the case with 
the waves resulting when a stone is thrown into water. 
Some kinds of rock seem more elastic than others, and so 
the concentric waves, instead of remaining circular in form, 
become irregular in shape. If the waves of water strike 
an unyielding surface, they are rejected, the reflected 
wave often crossing the original at oblique angles. Rock 
waves, it is thought, are similarly reflected, and some- 
times they produce effects that would seem as though 
there had been a vorticose, or whirling movement. 3 

Although the surface waves of earthquakes bear a close 
resemblance to the circular waves formed by dropping a 
stone in water, it must be remembered that they differ 
greatly in velocity and energy. The latter progress only 
a few yards a minute ; the former have the velocity more 
than double that of the swiftest projectile fired from a 
modern gun, travelling at a rate that varies from thirt} r 
to forty or more miles a minute. 4 The velocity of the 
wave depends partly on the elasticity of the material 



EARTHQUAKES 



97 



through which it travels, and partly ou the energy with 
which it is propagated. In hard, crystalline rock it travels 
rapidly and extends a great distance ; in sand and loosely 
coherent rock the velocity is much slower, and the waves 
quickly lose their 
energy. 5 

In the case of se- 
vere earthquakes a 
series of shocks fol- 
low one upon another 
with increasing in- 
tervals of time. 6 The 
first shocks are com- 
monly the most vio- 
lent. The duration 
of the shock is not 
perceptible to the 
senses for more than 
four or five seconds, 
but careful measure- 
ments by the seismo- 
graph, an instrument 
for the detection of 
shocks, show that it 
may last for more A ROCK column likely to be overturned 

. BY AN EARTHQUAKE 

than a minute. In 

many instances a Therock hasbroken away from the cliff, splitting along a 
naturally formed plane. H{ock waste, falling into the 

shock SeeniS to COn- crevice, has become saturated with water, which by freez- 
ing, has expanded and pushed the mass farther <md 

Sist Of a Single vio- farther from the cliff. 

lent thump. 7 

The focus of the shock may vary from a short distance 
to several miles below the surface; of the earth. The 
average distance is not far from six miles. The area 
involved in the earth-waves may be either circular or 




98 PHYSICAL GEOGKAPHY 

elliptical. 8 The diameter of the area seldom exceeds one 
thousand miles. 9 

Attending Phenomena.— Earthquakes are frequently 
attended by sounds. Sometimes the latter resemble low, 
rumbling thunder ; more commonly, however, the noise 
is like that produced when a heavily loaded wagon goes 
rapidly down a gravelled incline. 

In the great majority of earthquakes the effects are 
not severe ; they rarely extend beyond the stopping of 
clock pendulums, and the swinging of chandeliers, or the 
breaking of delicate substances. In severe shocks the 
walls of houses are wrenched and cracked, and the ground 
is fissured. In disastrous shocks buildings are shattered 
and the surface of the earth is seamed with deep fis- 
sures and chasms. In several instances lakes 10 have been 
formed or, perhaps drained, and stream channels changed. 

If the centre of the shock is in or near the ocean it is 
commonly followed by a series of gigantic waves, incor- 
rectly called " tidal " waves. Following the Lisbon earth- 
quake in 1755, enormous waves rolled in from the sea, and 
wrecked whatever the earthquake had left. 11 The ocean- 
waves that followed the earthquake at Arica, Peru, 12 car- 
ried the United States Steamship Wateree nearly seven 
miles inland, leaving her stranded in a dry stream bed. 

Cause of Earthquakes. — It is generally believed that 
earthquakes are the result of similar, but very rapid 
movements of the rock envelope that fold the strata into 
mountain -ranges and force molten lava from volcanic 
fissures. If the strata are slowly bent, no vibratory effect 
is noticeable, but if the strain increases until a fracture 
or a collapse takes place, the shock produces the vibra- 
tions that constitute the earthquake. 

When fissures are formed, usually one wall slips upon 
the other, so that the two edges are no longer in the same 



EARTHQUAKES 



99 



level. 13 The resulting inequality is called a fault, and 
wherever such faultings are found, they indicate, if not 
an earthquake, at least a surface disturbance. The ex- 
istence of such faults, therefore, is evidence that the outer 
shell of the earth is constantly under stress 14 at some 
point or another, and that the release of the strain pro- 
duces the earthquake. 




AN EFFECT OF THE EARTHQUAKE AT CHARLESTOWN 
The crack when first formed was about two feet wide. From a photograph. 

Distribution and Occurrence of Earthquakes.— No 
part of the earth is free from earthquakes, and recent ob- 
servations have shown that, in some part or other, they 
are of almost daily occurrence. As a rule, however, they 
are so feeble that scarcely one in fifty is noticeable, or 
even perceptible, without the aid of instrumental measure- 
ments. 15 

As in the distribution of volcanoes, earthquakes are of 
more frequent occurrence in younger mountain -ranges 



LrifC* 



100 PHYSICAL GEOGRAPHY 

than in the older ones. They are still less frequent in 
plains, unless the latter are undergoing a process of uplift 
or depression. They also accompany most volcanic dis- 
turbances. 16 

The study of several thousand earthquakes shows that 
shocks are a little more frequent when the earth is nearest 
the sun, and that they are also more prevalent when the 
moon is nearest the earth. 17 An explanation for this is 
not hard to find. Owing to the tendency to adjust itself, 
some part or other of the rock envelope is constantly under 
an increasing stress. But when the earth approaches 
either the sun or the moon, the increased mutual attrac- 
tion adds its force to the strain ; the latter is overcome, 
and a shock results. 

QUESTIONS AND EXERCISES.— If you live in the vicinity of a 
body of water, study the waves that form when a good-sized stone is 
tossed so that it falls vertically into still water. 

What is the relative position of the vertical and the horizontally 
progressive waves ? Repeat the experiment until the results obtained 
are familiar. 

If possible, clamp a brass or metal plate, about a foot square, to a firm 
table, so that the clamp holds the plate at its centre. Sprinkle dry 
sand on the plate and draw a violin bow across the edge. From the 
figures produced by the sand note the direction and character of the 
vibrations. 

COLLATERAL READING AND REFERENCE 

Rockwood. — Notes on American Earthquakes. 

Shaler. — Aspects of the Earth, pp. 1-45. 

Lb Conte. — Elements of Geology, pp. 154-171. 

NOTES 

1 Thus, the explosion under Flood Rock, for the purpose of 
clearing and widening Hell Gate Channel, produced an earth 
shock that differed in no material principle from those produced 



EARTHQUAKES 101 

by natural causes. The earth shock resulting from this explosion 
was recorded at a distance of nearly forty miles from Hell Gate. 
The velocity of the wave varied from 5,000 to 8,000 feet per 
second in the vicinity of the explosion. 

" The vibrations as they form underground are spherical waves 
and much like those formed in t*he air by the discharge of a fire- 
arm or the ringing of a bell. When the waves reach the surface 
of the rock envelope they spread out in the form of circular 
waves. 

3 Such waves have a terrific shattering force ; but those in 
which the horizontal and vertical components are combined are 
even more destructive : they not only shatter, but they produce a 
rocking motion as well. Vertical vibrations may only shatter a 
building ; a " roller " will not only shatter, but overthrow it. 

4 It has been calculated that the amplitude, or up-and-down 
motion, rarely exceeds one-quarter of an inch in height ; and or- 
dinarily, in severe shocks, it is seldom more than one-twentieth 
of an inch. The horizontal oscillation is scarcely more than half 
an inch, and even when it is not more than half as much, the 
shock has considerable shattering power. 

5 During the earthquake at Riobamba, Ecuador, a vertical 
movement of more than two feet is said to have been observed. 
The statement, however, is not considered authentic. At all 
events, the energy was sufficient to hurl heavy objects a hundred 
feet into the air. The bodies of men were thrown several hun- 
dred feet across the river. 

6 At St. Thomas, one of the Lesser Antilles, the shocks of 1868 
aggregated nearly three hundred in number. The earthquakes 
that shattered San Salvador, the capital of the State of Salvador, 
lasted for about ten days. The Charleston earthquakes did not 
cease for nearly a month, and a hundred similar instances might 
also be added. All this accords with the well-known law that a 
mass of rock envelope, in changing its foundations, cannot adapt 
itself to its new position at once, but does so little by little. 

' Many of the California earthquakes are of this character. 

6 The elliptical form is especially noticeable in mountainous 
areas, and in nearly every instance the major, or long diameter 
of the ellipse, coincides with the trend of the range or system. 
The reason therefor is the fact that the strata of rock are more 
elastic along thai) across their masses. 



102 PHYSICAL GEOGRAPHY 

9 In several instances, however, the area involved has far ex- 
ceeded this. Thus the shock that in 1755 destroyed Lisbon was 
felt at a distance of about twenty-five hundred miles. The sea- 
wave is propagated to a much greater distance. 

10 The earthquake that destroyed the city of San Salvador broke 
down the rim of a small lake and drained it. The famous earth- 
quake of New Madrid, Missouri, changed the level of the land to 
such an extent that a permanent swamp was formed in land that, 
before the shock, was high and dry. This area has since been 
known as the "Sunk Region." During the severest shock the 
current of the Mississippi is said to have been temporarily re- 
versed ; that it was greatly disturbed is shown by changes in its 
channel occurring at that time. Reelfoot Lake, in Tennessee, was 
considerably enlarged at the same time. 

11 Probably the most disastrous waves ever known to written 
history, however, followed this earthquake. After the town had 
been felled by shocks so terrific that thirty thousand people 
perished, most of the survivors took refuge on the massive sea- 
wall. Hardly had they reached it when the water began to re- 
cede, leaving the harbor dry. Then an enormous wave, sixty 
feet high, rolled in and completed the destruction, and thirty 
thousand more lives were swept out of existence before the 
waves ceased. At Cadiz the waves were thirty feet high, at 
Madeira eighteen, and along the Irish coast they were four or 
five feet in height. 

12 The sea-wave resulting from this earthquake crossed the 
Pacific Ocean and was recorded at Yokohama, Japan, twenty 
hours afterward. On the American coast the wave was observed 
as far north as Alaska, and to the eastward as far as Australia. 
The earthquake that in 1854 devastated a part of Japan was fol- 
lowed by a destructive wave. At Simoda the wave was thirty 
feet high ; at Peel's Island, one thousand miles away, it was 
fifteen feet ; on the California coast it was from twelve to 
eighteen inches in height. 

13 The destruction of Babispe, a small village in northern Mex- 
ico, is an excellent illustration. This disturbance, alleged to be 
a volcanic eruption, was in reality nothing more than a severe 
earthquake that levelled the buildings of the town. During 
the series of shocks a fissure was made, extending several miles 
in length, and when equilibrium was restored, the fissure had be- 



EARTHQUAKES 103 

come a fault — one side or wall being, in places, from ten to four- 
teen feet below the other. 

14 At Monson, Massachusetts, the rock in the granite quarries 
usually exhibits signs of heavy strain. Professor Isiles observed 
that pieces, before their ends had been detached, were split along 
a horizontal plane and bent upward at the middle. One mass, 
measuring 354 x 11 x 3 feet, increased an inch and one-half in 
length after it had been detached. These facts indicate the enor- 
mous pressure to which rocks may be subjected ; incidentally 
they show that even the hardest rocks are decidedly elastic. 

15 An instrument for measuring any of the elements of an 
earthquake shock is called a seismometer ; if it merely records a 
shock it is a seismograph. The horizontal element of the shock 
is recorded by means of a delicate pendulum carrying a pencil or 
stylus. The jar sets the pendulum in vibration, and the pencil 
records the direction of the oscillations. 

16 The sudden formation of gases on their rapid motion from 
one part of the volcanic district to another, will account for 
earth shocks at such times. 

17 Of a total of 364 shocks, 147 occurred in the Atlantic High- 
lands and Coar^t Plain, 06 in the Great Central Plain, and 151 in 
the Pacific Highlands. These figures have only an approximate 
value, however, inasmuch as many of the earth shocks occurring 
in the sparsely settled regions of the Pacific Highlands escape 
notice altogether. Of 66 shocks recorded in Canada, the United 
States and the West Indies during one year, 24 were in the At- 
lantic slope and the West Indies ; 3 were in the Great Central 
Plain ; and 39 in the Pacific Highlands, including Mexico and 
Central America. 




o * 

s -? 



CHAPTEE VII 

THE WASTING OF THE LAND : THE WORK OF 
RIVERS 

While various forces are at work wrinkling and folding 
the strata of the rock envelope, other agents are constant- 
ly at work wearing away those same folds and irregular- 
ities and wasting or degrading the surface of the land to 
its lowest, or base level. 

The principal agent in producing these effects is water, 
in one or another of its different forms. Falling on the 
land as rain it removes fine and loose particles of earth. 
It also sinks into the pores of the rock, perhaps dissolving 
some of it or, perhaps, freezing and breaking off small 
pieces. This process of degradation is called erosion. 
Gathering into swift torrents, the latter cut their channels 
deep into the surface, producing the effects called cor- 
rosion. Flowing against cliffs and banks or, perhaps, 
through underground channels, it saps the foundations of 
masses of earth and breaks them down by undermining. 

Gravitation is an aid in the process of degradation, 
for not only does the water invariably flow downward, 
but the detritus, or rock waste resulting, is likewise mov- 
ing to lower levels. Perhaps, for a time, it lodges in a 
hollow, or basin-shaped depression, until the latter is 
filled ; then the downward progress again begins. Of the 

105 



106 



PHYSICAL GEOGRAPHY 



water that falls from the clouds upon the land, 1 some 
evaporates and mingles with the air ; a part sinks into 
the ground, filling up the underground channels and res- 
ervoirs ; the remainder gathers into channels and flows 
back to the sea. 

Streams of water flowing upon the land are variously 




THE BEGINNING OF A LOOP— CUMBERLAND RIVER, KENTUCKY 
The river has built a flood plain on the west side and is cutting into the east bank. 



called rills, rivulets, brooks, creeks, and rivers — the name 
usually depending on the size of the stream. The largest 
streams are rivers. Almost every river is made up of 
branches and tributaries, and these, in turn, are fed by 
smaller branches — all together comprising the river sys- 
tem. The area drained by the river system is its water- 
shed 2 or basin, and usually the latter is surrounded by a 



THE WASTING OF THE LAND : RIVERS 107 

well-defined height of land, the ridge or divide that sep- 
arates it from adjacent basins. 

In some instances the crest of a mountain-range forms 
a divide, but in very many cases the latter is an almost 
imperceptible rise only a few feet high. 3 Thus, at Chi- 
cago, the divide between Lake Michigan and a tribu- 
tary of the Illinois River is only ten or fifteen feet high- 
er than the level of the lake. It must be borne in mind, 
however, that a high mountain-range is not necessarily a 
divide, for there are many instances where ranges are 
crossed by rivers. From any good map find the divide 
between the Susquehanna and Allegheny Rivers ; between 
the Great Kanawha and Ohio Rivers. Compare the divides 
with the ranges. 

Physiography of Rivers. — The beginnings of most 
large rivers are high in the mountains, where the rainfall 
is heaviest and the greatest accumulation of snow is found. 
The water that is let loose from a spring or from a 
winter's snowdrift trickles down the slope in tiny rills. 
On their way the rills unite into rivulets and brooks that 
tumble down the mountain slopes in self-made, pebbled 
gullies. 

Other streams join the brook and swell its volume into 
a mountain torrent that rushes down the steep incline, 
cutting its channel into hard rock and tossing to the one 
side or the other the obstacles in its way. Almost always 
it flows in a deep canon or gorge, the cutting of which is 
the principal part of its work. ' When the stream emerges 
from the mountain canon it is burdened with rock waste 
brought from the mountain side and, no longer able to 
carry all of this, because of the lessened slope, it drops 
the coarser material, forming a fan-shaped pile. Thence- 
forth, because it is no longer a swift torrent, it cannot re- 
move the heavier obstacles, but must flow around them. 



108 



PHYSICAL GEOGKAPHY 



The lighter rock waste, called sediment or silt, 5 is still 
carried by the flood of the river. Perhaps a little of it is 
dropped here and there, but the greater part is borne to 

the coast plain, 
which in many in- 
stances is the 
"made-land" 
formed of river 
sediments. After 
reaching the latter 
the silt is gradual- 
ly dropped until 
the river reaches 
tide-water. There, 
about all the rest 
of the silt is de- 
posited — either to 
be spread out in 
the form of a delta, 
or to be piled up 
near the shore in 
spits and bars. 

It is evident, 
therefore, that in 
streams which are 
degrading the land three processes are usually going on, 
namely — corrasion and undermining, transportation, and 
deposition. That is, from the moment the water touches 
the rock envelope it is picking up particles of earth ; it is 
carrying them downward; or else it is dropping them. 
Whichever it does, depends on the current. Increase its 
velocity and the water will pick up more particles ; de- 
crease the velocity and it will begin to drop them and 
flow around them. In the upper, or torrential part, most 




LOOPS AND CUT-OFFS OF THE LOWER MIS- 
SISSIPPI 

The abandoned channels arc sometimes called " Bayous ;' 
they form an intricate net-work of passages. 



THE WASTING OF THE LAND : RIVERS 1U9 



streams emphasize their right of possession by cutting 
their channels deeper. In the lower course the reverse 
is apt to be true; the stream clogs its channel with silt 5 
and is therefore compelled to make a new one on the one 
side or the other. 

In the study of such rivers as the Mississippi the rea- 
sons therefor are not hard to find. Because the slope of 
the plain through which it flows de- 
creases, the velocity of the current is 
checked, and because of the slackening 
current the water is constantly dropping 
its load of silt. 6 Moreover, when the 
latter has been dropped, the water can- 
not pick it up again unless the current 
is quickened, and must thereafter flow 
around it. 

Islands are common in rivers carry- 
ing a considerable sediment. The an- 
choring of a snag, or any other obstacle, 
slackens the current and causes the de- 
position of silt. The latter increases in 
amount until finally it reaches to the sur- 
face. Then vegetation gets root and an 
island results. 

The river which flows over a decreasing slope has a ten- 
dency, therefore, to form loops in its lower course, and in 
general the loops are long-lived. But when there is a 
succession of years of increased volume of water, the con- 
ditions are changed. Because the volume of water is 
increased the current is quickened, and the water then 
begins to pick up silt that it had previously dropped. 
In time, the neck of the loop is cut away, and the river 
shortens its channel — sometimes by twent\ T or thirty 
miles. 7 The line of moats, or oxbow lakes, along the lower 




Prairie du Chien 



ISLANDS IN A RIVER 



no 



PHYSICAL GEOGRAPHY 




PALMYRA BEND— NOW PALMYRA 
LAKE 



Mississippi marks the old loops and abandoned channels 
along this river. It is evident also that the great amount 
of silt removed when a loop is destroyed must be carried 

farther down stream and there 
deposited. How would this 
affect the river so far as the 
formation of bars is con- 
cerned ? As a matter of fact 
the destruction of a loop is 
attended by changes in the 
channel that are noticeable 
many miles both above and 
below the loop ; and more 
than a year elapsed after 
Davis cut-off had formed be- 
fore the changes ceased. 
If, during a period of sev- 
eral years, there is less than the usual rainfall, the stream 
will probably increase the amplitude of its loops, and 
even make new ones. With the coming of successive 
years of greater rainfall, however, the volume of water is 
increased, the current is quickened, and the water be- 
gins to pick up and remove sediment that formerly it had 
been unable to carry. 

Growth and Development of Rivers. — A river and 
its basin do not constitute a fixed, unchanging feature of 
the land. On the contrary, every river passes through the 
various stages of infancy, maturity, and old age ; and its 
legitimate work is to carve away and remove its basin 
until every part is worn away to base level. The moment 
any plain or surface — such, for instance, as the coast plain 
of New Jersey — is exposed to the action of the weather, the 
water falling upon it begins to form channels 8 and flow to 
the sea. Such a stream may be called an infant river. 



THE WASTING OF THE LAND : RIVEES 111 

At first the stream drains its water-shed very imperfectly. 
It encounters many obstacles; and if the slope is gentle, it 
finds not a little difficult}' in 4 _____ 

making its channel. It is em- ^^ a== -______j' 

barrassed by the inequalities THE LEGITIMATE WORK OF a*' 
of the surface, and because river 

Of them, lakes and SWampS It removes the rock waste from A to B : 

1 A B, the old ; a' b' , the new profile. 

form in the slight depressions. 

The channels are apt to be shallow and the divides between 
the adjacent branches are neither permanent nor well de- 
fined. In consequence, any unusual flood may result in 
the abandonment of an old and the selection of a new 
channel. Ked River of the North, is an example of an in- 
fant river. 

As a stream reaches maturity its character is changed. 
The channel is deepened and cut nearer to base level. 
The gullies of the tributary 
streams become ravines and 

many of the latter are sculpt- ,NFANT STAGE OF A RIVER 
ureel into broad valleys. The Thc strcai " ***$•*% £ cha "" d in the 
tributaries extend their chan- 
nels backward and not infrequently capture the waters 
of other streams less vigorous (See illustration, p. 100). 
The mature stage is the age of its greatest vigor and power. 
It may lengthen itself at both ends ; it may build a delta 
at its mouth and extend the latter seaward, or it may cut 
its headwater channels back- 
wards. 

The old age begins when THE mature and senile stages 

,,'.,. -, OF A RIVER 

the river has cut away and . T , • . ,,,,,, 

J vl - The mam stream ana its tributaries have 

trnimnnvfpd nil flip iviil'iKlo carved deep channels -in the plain A B : In 

uauspoiieu an tne avanaoie a , v c , lh [. remaining ,„„/.,,,,/ has bccn 
material within the reach of carrUd away - 
its various branches. Thereafter it can be revived only 
by a gradual elevation of some part of its bed, by changes in 



112 



PHYSICAL GEOGRAPHY 



its slope, or by a considerable increase of its volume. Just 
as a log moved against the saw results in cutting the tim- 
ber, so a gradual uplift of the stream channel gives the 
river fresh power and, for a time, rejuvenates it. An in- 
crease in the volume, by quickening the current of the 
stream, has also a similar effect. If, as in the case of the 




YOUNG RIVERS 

The stream on the right has uncovered the ledges of hard rock shown in the margin and 

falls have resulted. 



uplift of Uinta Mountains across Green River, the ele- 
vation is long-continued, just so long will the river be 
actively at work at that point. It can be rejuvenated 
along its whole course by the uplift or tilting of its water- 
shed in such a manner as to increase the current along the 
whole extent. Uplift is nearly always followed by exten- 
sive stream corrosion. 



THE WASTING OF THE LAND: RIVEKS 113 

Flood-Plains. — It often happens that a stream removes 
more material from its upper or torrential part than it can 
conveniently carry. The excess is then spread over the 
middle and lower parts of the basin, forming the " bottom 
lands " ox flood -plain. 

The deposition of sediment is the result of a slackening 




MATURE RIVERS 

The greater part of the basin of each has been removed. The tributary of the cen- 
tral stream is carving its way into the basin of the river on the right and will eventually 
absorb the head waters of the latter. 

of the current. In its infant stage the river has but lit- 
tle cutting power and usually can carry all the material it 
removes. When the headwater streams acquire greater 
vigor, however, they remove so much rock waste that in 
the middle and lower courses the water is overburdened 
with it, and the process of flood plain-making begins. 

Along that part of the plain occupied by the stream, un- 
less the current is increased, the deposition of sediment is 
constantly going on. The river builds its bed and banks 
a little higher than the level on either side, continuing the 



114 PHYSICAL GEOGEAPHY 

process until the coming of high water ; then it breaks 
through its self-made banks and selects a new channel in 
lower land. By this process of adjustment, the river, in 
turn, may occupy every part of its flood-plain. It there- 
fore follows that flood-plains are due to the overburdening 
of the current of the stream. 

In its relation to life and its industries, the flood-plain is 
the most important part of river physiography. The sur- 
face is always level, making the region accessible to trans- 
portation. Moreover, the rock waste is mixed with the ele- 
ments that form the food of plant life, and therefore the 
flood plain has a most fertile soil. In the Mississippi 




A FLOOD PLAIN 
The dark shading represents the sediment deposited by floods. 

Valley, for instance, where the bluff lands produce twenty 
bushels of wheat, the bottom lands yield thirty ; and if an 
acre of bluff soil yields one bale of cotton, the same area 
of bottom lands yields two. The greater part of the Chile 
of geography is a simoom-swept desert with scarcely a sign 
of life excepting that which pertains to the mines and the 
mountain valleys. The real Chile is found in the densely- 
peopled flood plains of the Andine streams. In these short 
valleys are concentrated nearly all the activities that go 
to make a great state. 

Neither do we find the Egypt of history in the broad 
stretch of land lying between the Red Sea and the Libyan 
Desert. On the contrary, the four thousand years of his- 
tory that has given to the world so much that goes to 



THE WASTING OF THE LAND: RIVERS 115 

make up modern civilization, belongs to the flood plain 
of the Nile. What has been the effect of the Mesopo- 
tamia on the history of the East? 

Terraces. — After a river has cleared away all the rock- 
waste and silt it can reach at the headwaters, the stream 
may then turn its cutting power against its flood-plain. 
Instead of depositing sediment, the water begins to re- 
move it. So it forms a deeper channel, along the sides of 
which a new and lower flood-plain is built. The new flood 
plain with the remnant of the old one form terraces. Of 
these there may be three or even four. Ultimately, how- 
ever, nearly or quite all the flood-plain is removed. 




TERRACES IN A FLOOD-PLAIN 
Each marks a stage of down-cutting. The darker shading sIwzl's the old bed of the river. 

It is evident, therefore, that flood-plains and terraces are 
merely incidents in the history of a river. Perhaps most 
of the rivers of the United States are in the flood-plain 
stage of their existence. Many of the streams of the north- 
eastern part are in the terrace stage and are approaching 
the period of old age. 

Deltas and Estuaries. — Salt water has a very remark- 
able effect in clearing muddy, fresh water, and the mo- 
ment the two mix the remaining silt held in suspension 
is quickly deposited. It follows, therefore, that, unless 
the sediment is swept away by currents and tides, a 



116 



PHYSICAL GEOGRAPHY 



considerable accumulation will form at the mouth of the 
river. 

The accompanying figure, the delta of the Mississippi 
River, shows one of the most interesting types of delta for- 
mation. It is evident, in this case at least, that the banks 
of the delta are self-made, and that they have been formed 
because the current has been checked more effectually at 







J>088 ' JETTTES 

South Pass 



A DELTA MOUTH : THE DELTA OF THE MISSISSIPPI RIVER 



the edges than in mid-stream. It is also evident that since 
the lower Mississippi has occupied its present channel, 
the river has built its lower part nearly one hundred miles 
into the Gulf of Mexico. 

The deltas of the Volga, and Ganges-Brahmaputra are 
considerably more intricate than that of the Mississippi. 
They are likewise older, and therefore more compactly 



THE WASTING OF THE LAND : RIVEKS 117 



filled with sediment. The delta of the Ganges-Brahmapu- 
tra is perhaps the most extensive known. Its frontage on 
the Indian Ocean is about two hundred miles, and its area 
about twice that of the State of Texas. Much of the land 
consists of shifting mud-flats, and the whole region is 
subject to destructive inundations. 

The delta of the Adige-Po has developed in a manner 
not unlike that of the Ganges. Probably no other river of 
its size in the world brings down more sediment than the 
Po. As a result its delta is filling and extending very 
rapidly — so rapidly, in fact, that the town of Adria (Had- 
ria), in Julius Caesar's time a seaport, is now more than 
twenty miles inland. Ostia, in 
early historic times, at the 
mouth of the Tiber, is now 
about seven miles inland. 

With respect to economic 
value, delta lands surpass al- 
most all others in the possibil- 
ities of productivity. The soil 
is exceedingly rich, and, because 
of the constant additions from 
the river, it is enriched as fast 
as its nutritive elements are 
taken up by vegetation. The 
Nile delta has long been known 
the granary of Egypt — the 



as 



Ganges- 




KP"*^ 



Sunderbunds of the 
Brah maputra are foremost 
among the great rice-producing 
fields of the world. 

An inspection of any good 
map will disclose the fact that while some rivers reach the 
sea, each through a delta, others equalty powerful with 



CHESAPEAKE BAY— AN ESTUARY, 
OR SUBMERGED RIVER MOUTH 

A part of a comparatively level plain 
has subsided below sea level. 



118 



PHYSICAL GEOGRAPHY 



respect to current, flow into estuaries. The Mississippi 
and the Delaware are contrasting examples. In the 
former case the river has a tendency to block its mouth 
with silt ; in the latter, a downward movement, or sink- 
ing of the coast has practically drowned the mouth of 
the river. Moreover, the action of the tide is usually 
strong enough to keep the channel clear of silt between 




A FJORD MOUTH OF A RIVER 
lis situation adapts it for the centre of commerce of a newly-settled region. 

bars. So, between the scouring action of the tide and 
the sinking of the valley there is not only a broad, but 
a deep area of water in most estuaries. If the mouth of 
the river is in a coast plain, the estuary usually takes the 
form similar to that of Delaware River. Along a rugged 
coast with an abrupt slope, however, the estuaries more 
commonly are like the indentations of the Maine coast. 
They are also numerous along the coast of Norway, where 
they are called fjords. 



THE WASTING OF THE LAND : RIVERS 119 

In rivers that flow into estuaries, the sediment is de- 
posited in the form of bars. In most instances two bars 
are formed, one at the mouth, the other at the head of the 
estuary. The reason for this double deposition of sediment 
may be found in the action of the tides. Bars are formed 
in comparatively still water, so, when the tide is slack at 
flood, the deposition takes place at the head of the estuary 
where the salt and the fresh water meet ; when the tide is 
ebb, the two waters meet at the mouth of the estuary and 
the deposition of sediment takes place at the lower end. 

It is evident that the estuary favors commerce and navi- 
gation while the delta on the whole is a hindrance. In 
the case of the Mississippi, the navigable channel of the 
delta has been kept open at an enormous expense. Of the 
great seaports that are centres of commerce, by far the 
greater number are on the shores of estuaries. 

Cascades and Rapids. — In flowing to lower levels, if 
the slope is abrupt, the water descends in a series of 
rapids in the form of reaches more or less terraced. The 
streams of the New England Plateau, and to a greater de- 
gree the torrents of mountainous regions are illustrations. 
In some instances, however, the stream plunges over a 
vertical embankment in the form of a cascade or fall. 
Of these, Niagara Falls, Spokane Falls, and those of the 
Zambesi River are illustrations. In some instances moun- 
tain streams make tremendous leaps. In the Yosemite 
Valley, Merced River in three plunges falls 2,600 feet ; and 
Bridal Veil fall, with a sheer pitch of 1,500 feet, reaches the 
lower level in the form of flue water dust. The Staubbach 
(" brook dust ") of the Alps is a similar cascade, having a 
fall of 900 feet. The Cascade Range of the United States 
and the Lauterbrunnen ("nothing but fountains") of Al- 
pine Europe are names that suggest the character of these 
regions. 



120 



PHYSICAL GEOGRAPHY 



In some instances the stream lias had little to do with 
making the cliffs over which it falls ; in other cases, how- 
ever, the river itself has made the falls. If a stream flows 
over the edge of a hard layer that rests on a softer material, 
the latter will be more quickly removed ; moreover, as the 
softer layer is worn away, the fall becomes greater and the 
water acquires an increased cutting power because it has a 
constantly increasing distance to fall. Finally the stream 




SECTION OF A WATERFALL 
The stratum at the top of the fall is harder and more resistant than the strata below. 

cuts away so much material at the lower level that a cata- 
ract results. 

In this manner the falls of Niagara River were formed. 
There is an upper layer of hard limestone surmounting a 
deep layer of softer rock. The upper layer offers consid- 
erable resistance to the water ; the lower layer is easily cut 
away. Hence the falls are increasing rather than decreas- 
ing in height. The upper layer, however, is worn not a 



THE WASTING OF THE LAND: RIVERS 121 

little, and the falls are receding up stream at the rate of 
nearly two and one-half feet a year. 10 

There are many cataracts, however, that are the result 
of accident. Thus, a flow of lava across Columbia River 
dammed the channel and formed the well-known cascades. 
A similar lava flood at the same time obstructed its chief 
tributary, the Willamette River, forming the cataract at 
Oregon City. 

Falls and rapids frequently occur in the terrace stage 
of rivers, although they may be developed in early matu- 
rity. They are rarely found in the flood-plain age, because 
the flood-plain buries all inequalities. After the stream 
has carved away its flood-plain, it may uncover and develop 
its former rapids and cascades. 

Migration of Divides. — As a rule, every stream works 
most actively in the upper or mountain part where its cur- 
rent is swiftest. As the various headwater streams deep- 
en their gullies they frequently extend them to a consider- 
able distance backward ; and a very vigorous stream may 
even cut its channel backward across a ridge or height of 
land. The latter then ceases to be the water-parting ; the 
divide therefore " migrates " or recedes from its former 
position. 

In cutting its channel backward across a ridge or height 
of land a stream sometimes captures and diverts a part of 
the feebler stream flowing on the opposite side of the chan- 
nel (See illustration, p. 109). Many of the " wind gaps " of 
the Appalachian region are the results of this sort of river 
piracy. They are abandoned stream channels — al >an- 
doned because the former occupant of each has been capt- 
ured further up the valley by a more vigorous stream that 
has crossed the height of land to get it. The Vistula 
River has probably obtained several of its headwater 
streams by the robbery of a neighbor, and at least one 



122 



PHYSICAL GEOGRAPHY 



stream in Northwestern Ohio and several in Pennsylvania 
seem to have suffered in a similar way. 

Unusual Adjustments. — In selecting a new channel 
or in adapting itself to the changing conditions of an old 
one a river is said to adjust itself. There are several 
causes which may compel a stream to change its course. 
It may clog its channel, or the latter may be obstructed 
by accident. Thus, by long-continued silting, the Hoang 
River, " China's sorrow," built its channel higher than 
the divide, near the top of which it flowed. In 1852, dur- 
ing a season of high floods, the river broke through its 
banks. Before that time it had flowed southeasterly from 




TUOLUMNE RIVER, CALIFORNIA 

The old stream channel is under the lava cap which forms Table Mountain . 
channels are at the base of the mesa. 



the present 



Kaifong into the delta of the Yangtze ; after the break its 
course lay in a northeasterly direction and the river now 
flows into the Gulf of Pechili. 

The flood of lava that formed the plains of the Colum- 
bia buried beneath it a long stretch of the river basin, and 
the river made a new channel around the lava flood. 11 
Tuolumne River, California, was similarly buried, but 
finally succeeded in making another channel through the 
obstruction. It is not unlikely that Saskatchewan River 
was cut in two by the rise of a height of land across its 
course, the water being ponded in Lake Winnipeg and 
then overflowing into Hudson Bay. 

Indirectly, man is responsible for the abnormal conduct 



THE WASTING OF THE LAND : RIVERS 123 

of certain rivers, and the cause thereof is the cultivation 
of the land. In order to make his land productive the 
fanner must not only clear it of growing timber and de- 
stroy the smaller vegetation, but he must also, in many 
instances, provide a system of rapid drainage. Because 
forestry, shrubbery, and sod all serve to retain water in 
the soil they therefore prevent rapid drainage. The re- 
moval of vegetation, on the contrary, has exactly the 
opposite effect. The rainfall is rapidly collected by the 
tributaries, and as quickly poured into the main stream. 
As a result, high and quickly-forming floods occur. 

The Ohio and the Susquehanna, especially in late years, 
have suffered much from disastrous floods, and these are 
mainly the result of deforesting their basins. Wooded and 
grass-covered slopes are slowly drained ; denuded slopes 
favor rapid accumulation of drainage waters. 

Geographical Distribution of Rivers. — Eivers are 
the offspring of rainfall and, as a rule, regions of great 
rainfall are regions in which rivers are largest and most 
numerous. This is shown in the case of the Amazon and 
the Kongo. Both rivers are situated within the belt of 
almost constant rains. Each has a large number of pow- 
erful tributaries, and each discharges an enormous quan- 
tity of water. 

A river cannot develop great length and size unless the 
water-shed that it drains has also a great superficial extent. 
When Columbus entered the mouth of the Orinoco, he at 
once declared the country southward to be a continent, 
for the reason that so large a river could not exist on a 
small body of land. 

There is no apparent law governing the distribution of 
rivers except the position of slopes and the amount of 
rainfall. The largest rivers are not in the largest conti- 
nents, nor are the longest streams in regions of greatest 



124 PHYSICAL GEOGKAPHY 

rainfall. The Atlantic receives the waters of more large 
streams than any other ocean ; the Arctic Ocean is the 
next in order. The reason therefor is the fact that the 
largest plains slope toward the one or the other of these 
two oceans. 

The great plains and slopes of the Western Continent 
receive the full benefit of moisture -laden winds ; and the 
rivers, as a rule, reach a higher state of development than 
those of the Eastern Continent. The Mississippi and the 
Amazon drain each a water-shed half as large as Europe. 
The Mackenzie, La Plata, Yukon, Columbia, and Colo- 
rado about equal in size the great master streams of the 
Old World. 

The broadest part of South America is crossed by an 
almost constant rain belt, and therefore is in the region 
of heaviest rains. The ocean winds traverse a sweep of 
about 2,500 miles before they are arrested by the Andes 
Mountains ; and because precipitation covers such an 
enormous area, there necessarily results a stream of vast 
proportions. As a matter of fact the Amazon discharges 
a greater volume of water than any other known river. 

The chief plain of the Old World faces the Arctic 
Ocean. It is the largest plain in the world, and is drained 
by large rivers. None of them equals the Amazon nor the 
Mississippi-Missouri, however, for the reason that they 
are situated in a region of very moderate rainfall. 

The southern part of Europe does not extend into the 
region of tropical rains ; hence the absence of large streams 
on the southern slope. The southern part of Asia is un- 
der the tropical rainbelt, but the drainage slope is com- 
paratively short, and but few large streams have formed. 
Thus it may be seen that the large plain of Eurasia is un- 
favorably situated for large rivers, while, on the other 
hand, the favorably situated areas are too small for the 



THE WASTING OF THE LAND : RIVERS 125 

development of great streams. The great number of 
smaller rivers, moreover, compensates for the absence of 
such rivers as the Amazon. 

Africa possesses several large rivers, two of which, the 
Kongo and the Nile, are of considerable interest. The 
Kongo, like the Amazon, is an equatorial stream, and 
the behavior of the two is almost identical. The Kongo 
is smaller only because its basin is smaller. The Nile 
is remarkable for its annual overflows, and from the fact 
that, in the lower 1,200 miles of its course it receives not 
a single tributary. 

Australia possesses but few permanent streams, and 
these are of small size. This continent is unfortunately 
situated. It is under the Calms of Capricorn, and it con- 
tains no high mountain range. The Murray-Darling is 
the only river of importance. In the summer season 
most of the streams disappear altogether, or else form a 
succession of shallow pools. 

Continental Rivers. — There are several large areas 
that have no drainage to the sea, and the rivers are there- 
fore called continental rivers. Where is the continental 
region of Eurasia ? It is drained by a multitude of riv- 
ers ; name the four largest. In Africa the only large con- 
tinental rivers are those flowing into Lake Chad. There 
are many continental rivers in Australia. Practically all 
of them are dry in summer and some are filled only when 
an occasional cloud-burst pours a flood of water into their 
channels. 

The Humboldt, Carson, and Jordan are the principal 
continental streams of North America. Describe their sit- 
uation from an}- convenient map. What do they indicate 
with reference to rainfall ? What would be the probable 
effect on these rivers if the Sierra Nevada ranges were no 
higher than the Appalachian Mountains ? In South 



126 PHYSICAL GEOGRAPHY 

America the Desaguadero, the outlet of Lake Titicaca, is 
the principal continental stream, although one or two of 
the larger rivers in Argentina are occasionally cut off 
from the sea. 

Economic Importance of Rivers. — Bivers are the most 
important highways of commerce and, in many ways, are 
the lines along which civilization and settlement penetrate 
to the interior of a country. Even at the present time 
merchandise can be carried by means of river navigation 
for less than the cost of transporting it in any other way. 
Most of the great migrations of peoples have followed the 
lines of rivers, and in mountainous regions the cultivated 
areas are confined mainly to river valleys. Outside the 
Great Central Plain of the United States most of the rail- 
ways of the country have been built along river valleys, so 
that these are practically " lines of least resistance " to the 
activities of a people. 

QUESTIONS AND EXERCISES.— Under what conditions and at 
what times is the stream with which you are best acquainted muddy ? 

Note and describe any place at which the stream is cutting away its 
banks. 

Note and describe some place where sediment is being deposited. If 
possible, account for the action in each case. 

An embankment of freshly turned earth receives the full force of a 
rainfall ; how will its general form most likely be affected ? 

What effect has sod, shrubbery, and forestry on a surface that is ex- 
posed to rain ? 

Name some results that might occur if the channel of a stream were 
blocked ? 

How would the Mississippi be affected if the Ozark highlands were 
elevated considerably higher ? (See any good topographic model or relief 
map.) 

What effect will the approaching old age of the Mississippi have on 
the size of the Gulf of Mexico ? 

On p. 1 13 is a map of Chesapeake Bay ; make a sketch-map and restore 
the river channels on the supposition that the surface were uplifted 
until about the lowest point is higher than sea level. 



THE WASTING OF THE LAND : RIVERS 127 

Does the appearance of the Canon of the Colorado River suggest an 
abundant or a scanty rainfall? How would a great increase in the 
rainfall affect the scenery so far as the topography of the valley is con- 
cerned ? 

What does the absence of tributaries indicate concerning the rainfall 
of the lower Nile ? 

From the cyclopaedia, or any convenient reference-book obtain a de- 
scription of the Volga and its delta. 

Make a list of ten or more important cities situated on estuary 
mouths ; — two on or near delta mouths. 



COLLATERAL READING. 

Shaler.— Aspects of the Earth, pp. 143-196. 

Mill.— Realm of Nature, pp. 241-251. 

Davis. — Rivers of New Jersey. National Geographical 3faga- 

zine. 
Redway.— Physiographic Geography of the Mississippi River. 

Proceedings Engineers' 1 Club, Philadelphia. 
Mississippi River Commission.— Map of the Alluvial Valley 

of the Mississippi River. 
Powell.— Physiography of the United States, Monograph II. 
Russell. — Rivers of North America. 



NOTES. 

1 On an average, about three feet of water fall each year on the 
land. The rate is not uniform, however, but varies from a frac- 
tion of an inch to about fifty feet. Directly and indirectly all 
the water of the land comes from the sea and, sooner or later, re- 
turns thereto. 

2 The term " water-shed " is often used as a synonym of "di- 
vide." Properly used, however, it is not a divide but a basin. 

8 There are a few instances in which the divide is so ill-defined 
that the same pool, pond, swamp, or stream may discharge its 
waters into streams whose mouths are at a great distance one 
from the other. Thus, Two-ocean Pond, in Yellowstone National 
Park, in high-water season, lias two outlets — one through the 
Yellowstone to the Mississippi, the other through the Columbia. 



128 PHYSICAL GEOGRAPHY 

In other words one has Atlantic, the other Pacific drainage. The 
Cassiquiare River bifurcates, discharging simultaneously into 
the Orinoco and the Rio Negro, a tributary of the Amazon. Be- 
tween the headwaters of the Parana, and those of the southern 
tributaries of the Amazon, the land is so flat that, in places, the 
drainage is undecided. 

4 The cutting and the carrying power of water depends on the 
speed of the current. A slight difference in the velocity makes a 
very great difference in its carrying power. Water flowing at the 
rate of four miles an hour will carry sixty-four times as much 
material as water flowing at half that rate of speed ; that is, the 
carrying power varies inversely as the sixth power of the velocity. 

5 Silt is the name commonly given to matter held in suspension 
in water ; sediment to material that has been dropped. The 
two words are often interchangeably used. 

6 Whichever process goes on at any particular locality depends 
on the velocity of the current. In seasons of high water the cur- 
rent may remove material, while at low- water stage it may form 
a bar. That is, the middle course of a stream extends much fur- 
ther down stream in high than in low water periods. In short 
streams that flow in channels of considerable slope there is prac- 
tically but one course. In rivers whose waters are habitually 
clear the " courses " are rarely ever well defined. 

7 Davis cut-off at Palmyra bend, near Vicksburg, Mississippi, is 
an example. The distance around the loop was twenty-two 
miles ; across the neck, it was scarcely half a mile. An obstruc- 
tion anchoring in mid-channel forced the current against the 
narrow neck, and the latter, little by little, was cut away by the 
stream. Finally the isthmus was severed and the whole flood of 
the river very quickly poured through the cut. Around the loop 
the fall of the river was about four inches per mile ; through the 
cut, over five feet. The river scoured its channel about one hun- 
dred feet in depth, and so swift was the current that more than 
a week elapsed before steamboats could ascend it. The effect of 
the cut-off was far-reaching, and extended both above and below 
Palmyra Bend a distance of over one hundred miles. 

8 Such a stream is sometimes called a consequent river because its 
formation is consequent upon the elevation of the plain. A river 
is an antecedent stream when its existence dates before that of 
some other feature, Thus Green River existed before the forma- 



THE WASTING OF THE LAND : RIVERS 129 

tion of Uinta Mountains, and with respect to them is an ante- 
cedent river. 

9 At the present time the real mouth of the Hudson is near 
Troy. Below this point the river is an arm of the sea, swept by 
tides throughout the whole distance. This singular condition is 
due to the fact that the lower part of the river has been sub- 
merged, since Glacial times. The explorations of the U. S. Coast 
Survey have disclosed the old channel of Hudson River from 
lower New York Bay a distance of nearly eighty miles to the 
southeast. Were this part of Atlantic coast again to be raised, 
it is not unlikely that the river would recover its long-buried 
channel. 

10 At the point where the angle in the ledge is formed, the reces- 
sion since 1875 has been more than two hundred feet ; at the 
American Fall, since 1842, it has been very slight. It is a ques- 
tion of time only until the Canadian Fall shall have receded to 
a line between Dufferin and Sister Islands. When this has taken 
place the American Fall will have nearly or quite disappeared. 
Had the conditions of a hard stratum at the top and a softer one 
at the bottom been reversed, there would now be no cataract, 
even had there been one at the beginning of the present epoch. 
The softer rock would have been worn away until the perpen 
dicular front had become an incline extending to a point below 
Whirlpool Rapids ; and instead of the sublime cataract, there 
would now be a succession of rapids like those which mark the 
passage of St. Lawrence River. 

11 In several other localities the Columbia has cut its channel 
through similar obstructions. In at least one case the river re- 
claimed its former channel by cutting through the entire thick- 
ness of lava, to a depth of about 2,500 feet ; at the two " cascades " 
the river is attempting to cut its channel through coulees of lava 
that flowed across its channel. Deschutes River, a tributary of 
the Columbia, is readjusting itself by cutting a new channel into 
the same sheet of lava. 



CHAPTER VIII 

THE WASTING OF THE LAND : THE WORK OF UNDER- 
GROUND WATERS 

Probably almost as much water sinks into the porous 
rock and the innumerable crevices of the rock-envelope as 
gathers iu the various external channels. The work of 
telluric, or underground waters may not be quite so active 
in degrading the rock envelope as are the surface streams, 
but they are nevertheless important factors in the physio- 
graphic processes that shape the earth's topography. 
Surface streams flow quickly away in their channels, but 
the underground waters must trickle slowly through chan- 
nels that are ill-adapted, spending their energy not only 
in forcing their way through passages that perhaps are 
self-made, but also in keeping the passages clear of ob- 
structions. The work of surface waters, therefore, is com- 
paratively easy and simple ; that of underground drainage 
is vastly more difficult. 

If the prevailing rock of a region be mainly of cla} r , or 
slate, or other impervious rock, the underground drainage 
will be close to the surface, 1 for such rocks not only pre- 
vent the passage of water, but they are also insoluble. In 
such cases the water must trickle through the top soil much 
in the same way that water passes through a filter made of 
sand and gravel — that is, it must flow in the spaces be- 
tween the particles of rock waste. 

On the other hand, if the rock of a region is mainly of 
limestone, and more especially if the strata be broken and 

182 



TTNDKWiROUND WATERS 133 

faulted, 2 underground drainage is apt to be very extensive. 
Not onl} - does the water clear a passage for itself along the 
lines where the rock is broken, but it also dissolves enough 
of the limestone to make caverns of vast extent. 

It must not be assumed, however, that these waters al- 
ways remain underground. On the contrary, they are con- 
stantly in motion, and they finally emerge from their chan- 
nels to reach the surface. In the study of underground 
waters they may be considered of three kinds, namely — 
jjercolatiug waters, springs and artesian wells, and under- 
ground streams. 

Percolating Waters. — When water sinks into porous 
ground it fills the spaces between the grains of sand, gravel, 



Water Level 
Springs 



DIAGRAM SHOWING THE FLOW OF PERCOLATING WATERS 

or other soil. Some soils are so porous that a cubic foot 
will contain more than one-quarter of its bulk of water. 
The latter sinks through the ground until it meets a layer 
of rock or clay through which it cannot pass. It therefore 
accumulates until its level is as high as the rim of the im- 
pervious stratum. 

Flowing over the lowest part of this rim, it goes on, per- 
haps to fill a similar basin lower down the slope, or possi- 
bly it comes to the surface in the form of a swamp, a pond, 
or a lake. If the plain or slope is traversed by a river val- 
ley a great deal of the water oozes through the soil into the 
stream. In many instances waters of percolation are the 
chief supplies of streams, 9 




134 PHYSICAL GEOGRAPHY 

Wells are always filled by percolating waters, and to ob- 
tain an abundant supply it is necessary only to sink a shaft 
to some point below the level of the water. Unless the 
well is so shallow as to catch the surface drainage, the water 
is usually cold and wholesome. The water of shallow wells 
is apt to be impure. 

If the area of porous soil is large and has a considerable 
depth, an enormous quantity of water may be held. The 
City of London, with its six millions of people,, is supplied 
with water that percolates through the adjacent chalk-beds, 
and the water supplies of many of the towns and villages 
of the high plains east of the Rocky Mountains are de- 
rived in a similar manner. 




THE WATER SUPPLY OF LOW SANDY ISLANDS 
The higher fresh water rests on the sea water. 

The " sand vallej^s " of Western Kansas, Nebraska, and 
Dakota furnish an excellent example of percolating waters. 4 
The storm waters falling in these valleys are almost all ab- 
sorbed and held in suspension by the deep deposits of light, 
pulverulent rock waste. During dry seasons the waters of 
these reservoirs are about the onty supply to the people 
living in that region. The amount thus held in the porous 
rock waste is generally sufficient to irrigate the crops that 
otherwise would perish from drought. 

The water supply of small and low islands is obtained in 
a similar manner. The storm waters fall on the island 
and immediately sink into the sand until they reach salt 
water. But inasmuch as the fresh water is the lighter of 
the two, it rests upon the surface of the salt water without 
mixing with the latter. 



UNDERGROUND WATERS 



135 



In man j instances the underground waters are confined 
between inclined strata of impervious rock. In such a 
case, if the porous layer be tapped by a boring, the water 
is forced up through the shaft to its normal level. Arti- 
ficial springs of this character are called artesian ivelh. 
The " driven " or " piped " wells so common throughout 
the Mississippi Valley and the prairie region are examples 
of such wells. They are shallow, however, and tap only 
the superficial percolating waters. The water, moreover, 
is usually brought to the surface by ordinary lifting pumps ; 
it is very rare that such wells are " spouters." 

In the case of wells sunk to a depth of two thousand 
feet or more, the water in many instances is thought to 




THE WATER SUPPLY OF ARTESIAN WELLS 
The porous stratum is both covered and underlaid with impervious rock. 



be forced above the surface — not by gravity, as is com- 
monly supposed, but by the pressure of the air or other 
gases within the reservoirs. 

Along the low coast plain of Southern California several 
hundred shallow artesian wells have been driven, and many 
acres have been made productive. The first wells were 
spouters, but at present, in nearly every instance the 
water must be pumped to the surface. Many such wells 
have been bored in the Sahara. 5 

Springs. — A small stream of water issuing from the 
ground is called a spring. In some cases the water spurts 
from a sloping wall, such as the face of a cliff, but in gen- 
eral, it gushes out of comparatively level ground near the 



136 PHYSICAL GEOGRAPHY 

foot of a slope. Usually the discharge does not amount to 
more than a few gallons per minute, but in a few instances 
it is sufficient to fill the channel of a good-sized stream. 6 

The storm waters that fall on porous soil sink until they 
come to rock through which they cannot pass, and, flowing 
along the surface of this impervious layer, finally emerge 
to the surface at some distance lower down. In the mean- 
time, if the water has been able to make a free channel 
instead of slowly percolating through the ground, it be- 
comes a spring. 

As a rule every spring makes its own channel. Usually 
the force of the flowing water is sufficient to carry away 
the lighter and finer material, thereby not only forcing a 
passage, but keeping it clear afterward ; but in many cases 
the water makes a channel by dissolving a part of the rock 
through which it flows. If the quantity of material dis- 
solved be considerable, mineral springs result. Such 
springs are very common. Those at Saratoga, Vichy, and 
Carlsbad, are known all over. the civilized world. 

In volcanic regions, where the rocks are apt to be seamed 
with fissures, the water trickles downward until it comes 
in contact with heated rocks, and when it again emerges 
to the surface the water may be at a boiling temperature. 

So long as the mouth of a spring is lower than the sur- 
face of the waters from which it is derived, the spring will 
continue to flow, and will be a constant spring. If it be 
situated in a region of periodical rains it is apt to be a 
periodical spring — flowing during the rainy season only. 
If the flow depends partly on the pressure of air or other 
gases, an intermittent spring may be formed. 7 

Geysers. — In several volcanic regions there are hot 
springs, which at intervals eject copious quantities of hot 
water and steam. The eruptions, unlike volcanic out- 
bursts, occur with almost clock-like regularity. 



UNDERGROUND WATERS 



137 



The geyser differs from other hot springs in having a 
long, irregular tube that extends deep into hot volcanic 
rocks. The tube is formed 
probably by the spring- 
water itself, which, when 
very hot, dissolves a con- 
siderable amount of the 
mineral silica but deposits 
it on cooling. 

The water that gradually 
collects in the lower part 
of the tube in time is heated 
far beyond the temperature 
at which water ordinarily 
boils. For a considerable 
time, the weight of the water 
in the upper part of the 
tube prevents boiling in 
the lower part. Finally a 
small amount of steam is 
formed, and some of the 
water is forced out at the 
top of the spring. As soon 
as this occurs, the pressure 
at the lower part being re- 
lieved, the water below, 
that has been heated far 
above the boiling point, 
flashes into steam — not 
gradually but instantly. 

Eruptive springs of this character are not common, and 
there are but three regions known in which they have been 
found— Iceland, Yellowstone National Park, and Northern 
New Zealand. Hot mineral springs occur in many other 




A GEYSER. 



YELLOWSTONE NATIONAL 
PARK 



138 PHYSICAL GEOGRAPHY 

localities, but they are not eruptive. The geyser region of 
Iceland has been known for more than a century. It is 
situated near the group of active volcanoes and covers an 
area of two or three square miles. There are about one hun- 
dred eruptive springs, one of which, Grand Geyser, spouts 
a column of water and steam to a height of one hundred 
and forty feet. The New Zealand group is situated near 
the volcano Tarawera. It is small in area, and contains 
but few spouting springs. 

The geyser region of the Yellowstone National Park, 
Wyoming, contains several groups, mainly in the basin of 
Firehole Biver. It comprises more than ten thousand 
geysers and hot springs. Of this number about two score 
discharge water to a height of one hundred feet or more ; 
one, the Giantess, spouts a column of water two hundred 
and fifty feet high, while the steam is forced nearly a thou- 
sand feet higher. The eruptions occur at periods varying 
from thirty minutes to about as many hours. Each is pre- 
ceded by a gentle overflow of water, and commonly lasts 
from a few seconds to fifteen minutes, but in a few instances 
continues for more than two hours. The intervals between 
eruptions rarely vary more than a few minutes, but care- 
ful observations show that their length is increasing, and 
the energy of eruption is diminishing. 

The deposition of silica from the cooling waters takes 
fantastic forms. In many instances the rock thus produced 
is richly colored with variegated bands. The " Pink-and- 
White Terraces " of New Zealand derive their name from 
this fact. 

Mud Volcanoes. — Mud " Volcanoes" are hot springs 
that have piled cone-shaped mounds of mud about their 
vents. The mud hardens into a compact mass. Steam 
and sulphurous gases are commonly the products of these 
alleged volcanoes. The energy displayed is feeble, and 



UNDERGROUND WATERS 139 

the mud cones are seldom more than twenty or thirty feet 
high. The mud consists of fine clay formed from the min- 
eral matter of the spring. Mud volcanoes are common in 
all volcanic regions. 

Underground Streams. — In addition to the multitude 
of surface streams, a large part of the water finds its way to 
the sea — not simply by percolation but in underground 
streams. Undoubtedly the run-off of most streams is 
mainly above ground, but, at the same time, a considerable 
part of their waters flow below the surface. 

There are several reasons for this. In the first place, 
whenever a stream flows in a gravelly channel, a great deal 
of the water must necessarily sink into the gravel and flow 
along the old bed-rock bottom. The same is equally true 
in the case of rivers that flow through light, sandy rock 
waste, such, for instance, as those of the Basin Region, 
west of the Rocky Mountains. The underground flow of 
such rivers is strong even when fierce summer heat has 
evaporated their surface waters. 8 

In many cases, too, small river channels have been ob- 
literated for one purpose or another. Now, although the 
surface flow may be destroyed the underground current is 
not ; on the contrary, it is apt to be strengthened. Thus, 
in some of the larger cities many small drainage courses 
have been covered up in grading the streets, and in several 
instances it has been found necessary to excavate these old 
water-courses and sewer them. 

In New York and London the channels of many such 
streams have been plotted, and drainage maps showing their 
former courses are used by the Boards of Health in sanitary 
investigation. In several instances these streams, becom- 
ing obstructed, have forced their way to the surface and 
flooded the streets with a deluge of water. Such experiences 
are not uncommon, they occur in almost every large city." 



140 



PHYSICAL GEOGRAPHY 



Of still greater interest, though not more important, are 
the various " Lost " rivers. These streams receive their 
name from the fact that for part of their courses they are 
ordinary surface streams ; for the rest, they now through 
subterranean channels. In some instances the water of 




A SINKHOLE, EDMUNSON COUNTY, KENTUCKY 
The throat leading to the cavern below lias been artificially closed. 



the river disappears by percolation ; in most instances the 
stream pitches headlong into a " sinkhole." 

In the limestone area of southern Indiana, Kentucky, 
and Tennessee, underground rivers are very common. 10 
One of these rivers winds its way beneath the floor of 
Mammoth Cave. Its waters contain a species of fish and 
two or three of insect life that have rudimentary eyes 



UNDERGROUND WATERS 141 

only — and indeed they have no use for perfect organs, for 
never a ray of light penetrates to their abode. 

Similar streams are found in Weir's Cave, in Luray Cave, 
and, in fact, in almost every limestone cavern. In Derby- 
shire, England, the Hampo and the Manifold flow many 
miles each through an underground passage. In both in- 
stances the identity of the stream is proved by throwing a 
floating body into the water above the beginning of its 
underground course and capturing it when it reappears. 

In Southern California, where water is required for ir- 
rigation, underground streams have been captured and 
forced to the surface. This is accomplished by building a 
dam across the stream at a point where it emerges from 
the canon to the open plain. The dam extends from the 
surface of the ground down to bed-rock. The water '..i 
thereby forced to the surface. 

It is noticeable that where such submerged dams are 
constructed, the artesian wells in the plain below are seri- 
ously impaired — the flow of water being greatly reduced — 
all of which seems to show that underground waters have 
a much greater circulation than is generally imagined. 

Physiography of Underground Waters. — Although 
the work of underground waters is by no means so extensive 
as those flowing above the surface, they are nevertheless of 
great importance especially from an economic point of view. 
Under almost any conditions water has a considerable sol- 
vent power, and hot water, especially if under pressure, will 
dissolve many kinds of rock that are not affected by cold 
water ; when the solution cools, however, much of this 
matter is again freed from solution. In the meantime, if 
the water has been forced to the surface, the substances 
dissolved will be carried along and there deposited. 

Sometimes the deposits are spread hap-hazard over the 
surface of the ground, forming sinter or tufa. If the latter 



142 PHYSICAL GEOGKAPHY 

happens to cover loose rock waste or soil, a cavern or cave 
will result if the material under it be removed. 

Iu other instances the hot waters, charged with mineral 
or metallic salts, flow into deep fissures in the rocks. As 
the water cools the soluble matter is deposited on the walls 
of the fissure until, finally, the latter is filled, thereby 
forming a mineral vein or lode. All through the various 




BLUE GROTTO, ISLAND OF CAPRI, ITALY 

mountain regions of the earth, gold, silver, copper, lead, 
and other valuable metals have been deposited in such 
fissures and veins. 11 Thus underground waters are a 
vehicle by which many useful metals are carried from the 
interior to the surface of the earth. 

Caverns. — Caverns and caves, although sometimes 
formed at the surface in the maimer already noted, for the 
greater part are formed underground by the action of 
•water. 12 The water merely dissolves the rock and carries 



UNDERGROUND WATERS 



143 



it off, leaving a cavern. Clay, 
slate, granite, and sandstones are 
not readily dissolved ; and in re- 
gions underlaid by such rocks, 
caverns are rare. Limestones, on 
the contrary, are quite soluble, 
and in localities where they are 
the prevailing rock, caves and 
caverns are common. In the cav- 
ern district of Kentucky, Tennes- 
see, and Virginia 13 small pieces 
of sharp flint are plentifully dis- 
tributed throughout the lime- 
stone. These are tossed about 
and carried along with the water 
and thus become powerful cutting- 
tools. 

Between the solvent power of 
the water and the incessant cut- 
ting done by the flint particles, 
the underground channel is worn 
deeper and wider till a cavern, 
perhaps a score of miles long and 
many feet deep, is formed. Very 
likely it has hundreds of galleries 
and branches ; time alone is nec- 
essary to give it vast dimensions. 

But time alone Avill see the fac- 
tors that made the cavern destroy 
it. In the first place the surface 
waters are constantly at work 
wearing away the rock that forms 
the roof or dome of the cavern. 
By and by breaks are made 



~\M 



144 



PHYSICAL GEOGRAPHY 



through the roof and sinkholes are thus formed. These 
increase in size and in number until the dome is destroyed. 
The river is then no longer an underground stream ; it is a 
surface river flowing in a limestone canon. Natural Bridge, 
in Virginia, is a remnant of one of these domes ; the rest of 
the roof has been carried away. 14 

In the second place, parts of these caverns are filled up by 




A PASSAGE IN LURAY CAVERN— STALACTITES AND STALAGMITES 

the limestone itself. In places the water charged with lime- 
stone leaks or filters through at the top of the dome, fall- 
ing drop by drop. A part of the water leaves a minute 
portion of limestone at the roof ; the rest falls to the floor 
of the cavern, where a little more of the water evaporates. 
So, little by little, the deposited limestone gathers into 
icicle-shaped columns, both at the roof and the floor of the 



UNDERGROUND WATERS 145 

cavern. The former are called stalactites, the latter stalag- 
mites. In time the two join, forming a single column, and 
as the water trickles down their sides they increase in size, 
and thus the cavern is filled. 

Perhaps, in the course of time, this same mass of lime- 
stone may be dissolved away and redeposited elsewhere. 
At all events, the process illustrates the general law that 
governs cavern-formation in these regions. Water in mo- 
tion dissolves limestone and makes caverns ; still water de- 
posits limestone and fills them iqj. 15 

QUESTIONS AND EXERCISES.— If possible find the depth of each 
of half a dozen or more wells in the neighborhood in which you live : 
compare the distance of the surface of the ground to the surface of the 
water in the wells. 

To what depth must a well be sunk before it will fill with water ? 

Will one be apt to find percolating waters in regions having but a 
very little rain ? 

Explain why water in very shallow wells is apt to be impure 

How do springs become " mineral " in character ? 

Why does rain water contain no mineral matter in solution ? 

Why are geysers and hot springs confined usually to volcanic regions? 

Under what circumstances or conditions can water be heated above 
the ordinary boiling point ? (See almost any text-book in physics.) 

From the diagram, p. 129, decide the conditions which will cause 
underground streams or percolating waters to form a swamp. 

Describe a way in which caverns may be formed at the foot of sea 
cliffs that face heavy waves. 

How are the sinkholes in the limestone regions formed ? 

By using lime-water such as is obtainable at the druggist's, suggest 
a way in which stalactites may be artificially formed. 

COLLATERAL READING. 
Shaler. — First Book in Geology, pp. 66-87. 
SHALKR. — Aspects of the Earth, pp. !l(i-142. 
POWELL. — Irrigation and Artesian Wells, pp. 203-290. United 

Males Geological Survey, 11th Annual Report, Part 2. 
Lk COXTE. — Elements of Geology, pp. HW-1 l:{. 

United States Geological Survey. — Map of Yellowstone 
National Park. 



146 PHYSICAL GEOGRAPHY 



NOTES. 

1 If the rocks are near the surface and the amount of water is 
considerable, swamps may result. That is, swamps may be an 
incident of imperfect underground drainage, as they are of im- 
perfect surface drainage. 

2 The fissures between the ends of faulted strata are very fre- 
quently the channels of springs, and sooner or later the fissure is 
likely to be closed up by deposits from the spring water. 

3 This may be seen in the cases of streams that flow through a 
region of pervious soil. Such streams steadily increase in volume, 
although for many miles they receive no tributaries. As an ex- 
ample, Spanish Fork, on the west slope of the Wasatch Mountains, 
receives only two or three small tributaries from the summit to 
the base of the mountains. It begins as a rivulet, scarcely larger 
than one's arm ; it reaches the base of the range, a mountain tor- 
rent twenty feet across. Almost the whole increment is due to 
percolation. 

4 The sand valleys are apparently hills, but, in most cases 
they are valleys filled with rock waste carried thither by winds. 
In the saturation of these accumulations of rock waste capillary 
attraction is an important factor ; for this little-understood 
force is not only an agent of accumulation, but one of reten- 
tion also. 

5 The amount of desert land made productive solely by artesian 
wells has been greatly exaggerated by senseless guesses. Such es- 
timates commonly make the aggregate as "millions of square 
miles." As a matter of fact all the artesian wells in the world 
do not supply an area equal to that of the State of Delaware with 
the water necessary to produce the whole of its crops. 

6 The difference between springs and percolating waters is 
mainly one of degree ; issuing from a channel it is a spring, but 
if the water merely oozes through the soil it is considered only 
as an example of percolation. In Florida there are a number of 
springs, so-called, that discharge each an amount of water suffi- 
cient to fill a river bed. Orange and Silver Springs are so large 
that small river craft easily enter the mouths. These springs, as 
a matter of fact, are the exits of underground rivers. 

7 From time iminemoi-ial geographers have explained the peri- 



UNDERGROUND WATERS 147 

odical spring on the supposed existence of a siphon-shaped chan- 
nel. Doubtless such channels exist, but not a single one has ever 
been discovered. In a few instances the pressure of accumulating 
gases is known to be a cause of intermittent flow, but in the great 
majority of cases the cause of periodicity is unknown. One of the 
most remarkable periodical springs occurs in Palestine near the old 
convent of Mar Jirius. This spring is quiescent for about two and 
a half days, and its period of activity lasts tor several hours. It 
is probable that the stream flowing from this spring is the Sab- 
batic River described by Josephus, which rested for six days and 
flowed on the seventh. The fact that such springs gradually de- 
crease their periods of quiescence, and finally become regular, 
bears out this supposition . A spring near Rogersville, Tennessee, 
is celebrated for the enormous quantity of water ejected. Its 
period of flow occurs about every half hour, lasting only a few 
minutes. The Bullerborn, once a famous intermittent spring of 
Westphalia, has now a constant flow. In regions of very high 
tides, periodical springs are sometimes formed by tidal action. 
The fresh water is pushed back by the tide, until it emerges to 
the surface through self-made channels. 

8 In desert regions, where the heat is intense, there are many 
instances of rivers that are dry "washes" in the daytime, and 
fair-sized streams at night. Water nearly always can be found 
at a slight depth, by digging for it. In the daytime, the enor- 
mous evaporation causes the water to disappear. In the night, 
or during cloudy days, the evaporation is lessened and the perco- 
lating waters rise to the surface. This phenomenon is occasion- 
ally noticed in the lower courses of Humboldt, Carson, and Reese 
Rivers, in Nevada. The underground part of the river is nearly 
always to be found. 

,J Considerable trouble from this cause occurred near the junc- 
tion of Oxford Street and Edge ware Road, London, and the rea- 
son was the fact that the famous Tyburn flowed in this locality, 
crossing Oxford Street a little to the eastward of the entrance 
to Hyde Park. About four hundred square feet of Broad - 
way, New York, recently caved in from a similar cause. The 
foundations of a costly church in Philadelphia sank in the 
quicksand before they were completed, and the large sewer under 
one of the principal streets has caved in several times— all be- 
cause they were undermined by buried si reams. 



148 PHYSICAL GEOGRAPHY 

10 At Orangeville, Indiana, an underground stream comes to 
the surface and flows with sufficient force to turn a mill-wheel. 
Only a few miles away, Lost River, a considerable stream, sinks 
out of sight. San Pedro Springs, near San Antonio, Texas, 
is the outlet of an underground stream. Giant Spring, near 
Great Falls, Montana, is the outlet of Little Belt River, which 
disappears and flows underground for thirty miles of its course. 
In Alabama, the engineers of the Anniston and Atlantic Railway 
discovered an underground stream sixty feet below the bed of 
Coosa River. According to Greek legends, the Alpbeus, the river 
of Peloponnesus, which Hercules turned through the Augean 
stables, sank underground and emerged to the surface somewhere 
in Sicily. As a matter of fact a considerable part of the course 
of the Alpbeus is underground, and there is a spring in Sicily 
discharging a large volume of water. It is hardly necessary to 
add that the two have no connection. 

11 As a rule such veins have a very symmetrical banded appear- 
ance, the stripes on the right hand corresponding with those on 
the left. In California, these veins are called "ribbon " rock. 

13 There are several instances in Which caves have been formed 
in volcanic rocks. Fingal's Cave, on the Island of Staffa, west 
of Scotland, is an example. It is more than two hundred feet in 
length, and is surmounted by a dome sixty feet high. In many 
instances waves have hollowed out caverns in rock cliffs. 

13 Mammoth Cave, Kentucky, is a labyrinth of passages aggre- 
gating more than two hundred miles ; the length of the cave on 
a straight line is about ten miles. Some of the vaults and domes 
are two hundred and fifty feet high. There are several other 
caves in the vicinity nearly if not quite as large. Weir's Cave 
and Luray Cavern, both in Virginia, are smaller than Mammoth 
Cave. Being limestone caverns they do not differ from the latter. 
Howe's Cave, Schoharie County, New York, is one of the few 
large caverns of interest in the northern Appalachian i-egion. In 
the grotto of Lueg, lllyria, there are three galleries, one over 
another. The cavern of Adelsberg, Austria, is the abandoned 
channel of the Poik. Its length is not far from two miles ; its 
labyrinthine passages aggregate many miles. A considerable 
part of the course of the Poik is underground. Probably the un- 
derground passage and caverns of the Timavo have been more 
thoroughly investigated than those of any other stream. The 



UNDERGROUND WATERS 149 

river flows to the Adriatic, a few miles north of Trieste, and its 
character has been known for more than two thousand years. 
Concerning it Virgil wrote : 

. . et fontem superare Timavi 
unde per ora novem vasto cum murmure montis 
it mare proruptum, et pelago premit arva sonanti. 

—JEneid I., 247. 

Virgil's description is no longer true of the delta, for the nine 
mouths have become only three in number. 

14 Many similar natural bridges are known to exist in various 
parts of the world. Near Bogota, Colombia, a natural arch spans 
a chasm nearly four hundred feet deep. The arch is a double 
one, the lower one being composed of three large fragments that, 
detached from the upper arch, fell in such a manner as to wedge 
themselves between the perpendicular walls. In one of the deep 
canons of Arizona a huge mass of rock has fallen and become 
wedged between the walls of the chasm, thereby forming a sort 
of natural bridge. A natural bridge spans Pine Creek, in Gila 
County, Arizona. Like that in Virginia, it is the fragment of the 
dome of a stream that once flowed underground. The arch is 
about four hundred feet wide and the span is about a thousand 
feet in length. The underside of the arch is water-worn, but 
since it was formed the creek has cut its channel more than two 
hundred feet downward. In several instances the arch more 
properly constitutes a tunnel. One, near Clinch River, Virginia, 
is more than halt a mile long, and is a part of the route selected 
for a railway. In almost every instance a stream of water Hows 
under the arch, and its current carries away the fragments that 
fall from the roof. 

15 The distribution and also the concentration of certain eco- 
nomic minerals, in many instances, has resulted from the flow of 
underground waters. Gold has been dissolved from certain rocks 
and gradually concentrated in veins through their action. Iron 
salts have been leached from rocks and deposited in other rocks 
by the same agency. Beds of sand through which water con- 
taining lime percolates, in time, become sandstone, the grains of 
sand being cemented together by the lime carried in the water. 



CHAPTER IX 

THE WASTING OF THE LAND: THE WORK OF 
AVALANCHES AND GLACIERS 

A great deal of the moisture mingled with the air falls 
upon the land in the form of snow. Excepting very cold 
regions, the snow that falls at altitudes below three or 
four thousand feet melts with the coming of spring and 
flows away in the various stream channels. In high 
mountain regions more or less snow falls at altitudes in 
which the temperature is rarely higher than the melting 
point of the snow. In such localities, therefore, but little 
of the snow can melt where it falls. 1 

In the Alps and in the higher ranges of the western 
United States, the heaviest snows fall between the altitudes 
of six thousand and nine thousand feet. Very little accu- 
mulates below four chousand feet, and but little falls above 
twelve thousand feet; in fact but little moisture exists at 
such high altitudes. 

At high elevations, even though the fall might be slight, 
it would seem as though the accumulation would increase 
until the mass of snow exceeded that of the mountains. 
In certain polar lands it is possible that this may be oc- 
curring, but in high mountain regions various agencies 
operate to prevent such enormous accumulation. Among 
them are evaporation, wind, avalanches, and glaciers. 
They not only remove the snow and ice, but they are also 
powerful factors in wearing away the land and in trans- 
porting rock waste. 

150 



WORK OF AVALANCHES AND GLACIERS 151 



Evaporation is a very active agent in the removal of 
snow. Ice and snow evaporate jnst as does water ; and 
at great heights, where the air does not press so heavily as 
at sea-level, evaporation is very rapid. This is seen when 
frozen roads become dry and dusty Avithout thawing. 2 

Winds are also a very potent factor. In high mountain 
regions the wind has a force that is almost unknown in 
lowlands, and the gales that rage among snow-covered 
peaks quickly clear the dry snow-dust from every exposed 
surface aud drift it into ravines and canons. 3 

There are two factors at work, however, that are inter- 
esting, not only because they remove an enormous amount 
of snow, but also because in transporting it they become 
physiographic agents of 
very great importance. 
These are avalanches 
and glaciers. 

Avalanches. — When 
a great body of snow, 
resting on a steep slope, 
suddenly slips and 
plunges down the in- 
cline, the moving mass 
is called an avalanche, 
or challanche. Excepting 
the matter of the mate- 
rial transported, which 
is mainly snow, the ava- 
lanche does not differ 
materially from an ordi- 
nary landslide. But 
while it is very rare that a second landslide takes place 
in the same track, it is evident that an avalanche may 
occur every time the snow falls on the slope. The snow 




AVALANCHE BASIN, MONTANA 

The slopes are too steep lo permit the accumulation 
of snow, ami the latter, gathering within the 
basin, hai formed the lake at the bottom of the 
cliff. 



152 PHYSICAL GEOGRAPHY 

accumulates on the steep slope imtil its great weight 
causes it to slip, and the great mass, gathering speed, 
moves downward with a terrific roar. 

In the Alps, where, as a rule, the slopes are steep, 4 such 
downfalls take place frequently and regularly. In many 
places the avalanche tracks are as definitely marked as the 
river channels. Indeed, one may consider the avalanche 
track as the torrential part of a stream whose flow is occa- 
sional and spasmodic. Like the mountain torrent, too, it 
carries to lower levels an enormous amount of rock waste 
stripped from the slopes. Not only are avalanche courses 
distinctly marked, but expert mountaineers who have ac- 
quired experience in discerning weather signs are able to 
predict the occurrence of the snowslide with great cer- 
tainty. The avalanche, therefore, is a feature of mountain 
economy not less normal than the mountain torrent. 

The most destructive avalanches occur in the first hours 
of sunshine, just after a snow-storm. 5 The flakes are then 
so fine and smooth that they have but little coherence, and 
almost any disturbance may start them. The footstep of 
the chamois or a gust of wind imparts motion to a handful 
of snow, and it begins its descent. Gathering fresh mate- 
rial as it advances, and increasing in velocity every moment, 
it soon becomes a force that sweeps everything before it, 
carrying havoc and destruction perhaps into the region 
of cultivated fields and human habitations, far beyond the 
foot of the slope. Rocks crash right and left and the whirl 
of the wind carries eddies of snow a thousand feet or more 
into the air. 

When avalanches follow their customary tracks they are 
neither especially dangerous nor destructive, unless the 
snow and rock waste reach beyond their ordinary limits. 
But in many instances they have taken place in localities 
previously free from them, and these are the cases in which 



WORK OF AVALANCHES AND GLACIERS 153 

the destruction is greatest. Not only is everything de- 
stroyed along the path of the moving snow, but the effects 
are even more apparent along the edges; for the blasts of 
wind set in motion by the swiftly moving snow, fell every 
vestige of timber a thousand feet or more on both sides. 
In recent years, places that the experienced mountaineers 
have discovered to be possible avalanche tracks, have been 
artificially guarded, so as to prevent the formation of 
dangerous snowslides. 

Another form of avalanche occurs in the Alps late in 
the season, at the beginning of warm weather. Instead of 
light, powdery snow, its volume consists of ice and coarse 
snow mixed with rock waste. 6 The lower part of the snow 
and ice are undermined by water as the ground on 
which it rests thaws. Finally the whole mass slides down 
the incline. These avalanches do not differ in any ma- 
terial respect from landslides. 

Glaciers. — A great part of the snow that falls on high 
and steep slopes is either blown into ravines by the wind 
or is tumbled into them by avalanches. In the upper 
part of the ravine the snow is light and flaky, but farther 
down it has begun to melt, and instead of ciystals it con- 
sists of little granules of ice, called neve. Still farther 
down the ravine, the neve has a striped or banded appear- 
ance. 7 Then the surface takes the form of irregular Avave- 
shaped ridges, and finally the surface is a field of ridges 
and hummocks, 8 half-drowned in streams of muddy water, 
and ending in a mountain torrent. 

All this mass of ice and snow constitutes a glacier. It 
is in motion, and excepting the velocity, which is so slow 
as to be almost imperceptible, its movements are much 
like those of a stream of water. The flow is faster at the 
surface than at the bottom, and it is also swifter in mid- 
stream than at the edges. 



WORK OF AVALANCHES AND GLACIERS 155 



Because the glacier moves more rapidly in the centre 
than at the sides of the stream, the surface is scored with 
cracks and chasms called crevasses. These are roughly 
parallel and cross the glacier in lines which, in many in- 
stances, point upstream. 9 In some cases the crevasses form 
gently curving parallel lines that are not unlike the rip- 
ples in a river. Ordinarily, the crevasse is narrow and 
only a few feet deep ; but in some places it becomes a 
chasm fifty or sixty feet from top to bottom. Crevasses 
are most numerous in that part of the glacier where the 
slope is the steepest ; and, in general, they mark wdiat in a 
river would be the rapids. The velocity of the current 
varies. On a gentle 
slope it may not be 
more than three or four 
inches a day ; on a 
steep incline it may be 
half as many feet. In 
summer, when the tem- 
perature is above the 
freezing point, the mo- 
tion is much swifter 
than in winter — in some 
instances twice as great. 

As the ice-stream 
makes its way down the 
ravine, fragments of 
rock fall from the con- 
fining banks and lodge 
at the edges. In time, these accumulate until they form 
walls of considerable regularity. These walls constitute the 
lateral moraines of the glacier. If two or more glaciers 
flow into the same ravine, the moraines on the sides that 
join unite to form a medial mora inc. In some instances 




CREVASSES AND MORAINE, NISQUALLY 
GLACIER. 



156 PHYSICAL GEOGRAPHY 

several medial moraines may be seen stretching with great 
regularity for a long distance. 

Toward the lower end of the glacier, much of this sort 
of rock waste gets to the bottom, in front of the ice-stream. 
In summer, when the lower end of the glacier melts to a 
considerable distance up-stream, the rock waste, consisting 
mainly of large bowlders, is strewn along the bed. But in 
winter, when the ice-front again advances, the scattered 
bowlders are pushed forward, forming across the path of 
the glacier the long windrow of rock waste that constitutes 
the terminal moraine. 

The moraines of a glacier are one of its most interest- 
ing and important features. Not infrequently the shape 
of the ravine is such that the rocks composing the lateral 
moraine are pushed against the sides, forming walls as 
regular as though they had been laid by human hands. 
Moreover, while the lateral moraines may decrease in size, 
the terminal moraine is constantly growing in volume. 

Glacial Ice Sheets. — Glacial movements are not con- 
fined to the ice streams of ravines, however. The sheet of 
snow that projects over the edge of a roof is a perfect 
illustration of glacier motion ; and so, too, is the patch of 
snow on a steep hillside that gradually creeps downward 
or acquires a distorted shape. 

But there are remarkable fields of ice many miles in 
extent, that exhibit all the phenomena of glacier move- 
ment. These vast fields are found mainly in polar regions. 
They are not confined between the sides of ravines ; they 
are ice sheets of vast extent. Probably the greater part 
of the sheet is gradually settling downward ; certainly the 
ice in many places is projecting beyond the edges and 
breaking off. 

The Greenland ice sheet is a striking example. To the 
best of our knowledge, almost the entire island is covered 



WORK OF AA T ALANCHES AND GLACIERS 157 

with ice and snow that have been accumulating during 
long periods of time. So far as known the only rock 
that reaches above the surface of the ice is found near 
the coast, where the ice-covering is thinnest. 

Along the southern coast much of the ice and snow dis- 
appears by melting. Farther north, however, the ice 
reaches the coast — sometimes descending into the fjords, 
sometimes presenting an unbroken wall from five to fifty 
miles in extent. In places the flow of the ice is compara- 




BIRTH OF THE ICEBERG 
The buoyant force of the water is shearing the fragments, and the latter float away. 

tively rapid — as much as forty or fifty feet a day. The frag- 
ments broken from the ice front are icebergs. Sometimes 
they tumble from the top ; in other instances the edge of 
the sheet is pushed out so far that the buoyant force of the 
water breaks a fragment from the sheet, and it floats off. 

Humboldt Glacier, on the west coast of Greenland, is a 
striking example of the ice-sheet. For a distance of about 
sixty miles, its ragged front, broken here and there by 
rock-cliffs, forms a sea-wall in places several hundred feet 



158 PHYSICAL GEOGRAPHY 

high. By far the most stupendous examples, however, 
are those of antarctic regions. Apparently the ice-sheet 
is continental in size and, judging from the thickness of 
the icebergs, it is probably several miles thick. 

Occurrence of Glaciers. — In general, glaciers begin 
above the line of perpetual snow and extend usually a 
short distance below it. In high latitudes, where the 
weather is cold, they occur at no great altitude above sea- 
level, but the nearer they are to tropical regions, the 
higher the altitude. In low latitudes they rarely occur 
below the altitude of fifteen thousand feet, while in polar 
regions they usually flow into the sea. 

The largest stream or ravine glaciers known are in the 
Himalaya Mountains; the best known are those of the 
Alps. Along the northern coast of Norway there are fine 
examples ; in the Patagonian Andes, and along the 
Alaskan coast, almost every arm of the sea contains one or 
more of them. Study the character of these coasts on a 
good map. In the Rocky Mountains there are numerous 
glaciers, but none of them is of great size. Several of the 
glaciers of Mounts Shasta and Tacoma (Rainier) rival the 
Alpine ice-streams in extent. Muir Glacier, Alaska, has 
a frontage of two miles on the sea. 

Most of the rivers flowing from the high slopes of 
mountains that reach above the snow-line have their sources 
in glaciers. Find examples in the Alps. 

Physiographic Effects of Glaciers. — The results of 
glacial action are readily observed in the glaciers of the 
present time and, indeed, they are so full of character that 
they are a most excellent key whereby the stupendous 
effects of the glaciers of prior geological times have been 
studied. 

The chief effects of glacial action are erosion and trans- 
portation. Ice alone is so soft that it has little or no 



WORK OF AVALANCHES AND GLACIERS 159 

wearing effect on bard rock, but if a moving mass of ice 
drags or pnsbes fragments of rock along at tbe sides and 
bottom it becomes a cutting tool of great power. It 
planes, gouges, or scratches, according to the character of 
the rock over which it moves. 

All through the northern United States and Canada, 
nearly to the Rocky Mountains, the surface has been 
scoured by glacial ice, and many thousand lake basins 




REGION OF GLACIATION IN THE UNITED STATES 

The heavy line shows the limit of terminal moraines : erratic bowlders occur in occasional 
localities a little farther south of the line. 

have been made or shaped. In the exposed rock of New 
England and New York, the grooved and rounded surfaces 
are one of the most marked features, and everywhere the 
erosion is so characteristic as to reveal its origin. The 
northern Appalachian Mountains were worn and broken, 
and the wide gap between the Adirondack and Catskill 
ranges — both groups being parts of the Appalachian folds 
— was probably made at this time. What has been the 



160 



PHYSICAL GEOGRAPHY 



effect of this gap on the commercial development of New 
York? That the surface of the ice-sheet did not reach 
quite to the top of the highest peaks of the Adirondack 
and White Mountains is inferred from the fact that certain 
alpine species are still found at their summits that do not 
occur at a lower level. 

The same markings are equally plain throughout north- 
ern Europe, and , the coasts of Norway and the British 
Isles probably received their present frayed and ragged 
appearance at the same time that so much of North 
Amercia was covered with glacial ice. 




A DRUMLIN 
/;; many instances the surface is covered with fertile soil. 

The transportation of material is a still more noticeable 
effect of glaciation, and the rock waste that has been 
removed, is commonly known as drift. Glacial drift is 
unsorted material, and in size the pieces vary from grains 
of sand to bowlders weighing several thousand tons. In 
character, the gravel of drift differs materially from stream 
gravel ; for while the latter is composed of uniformly 
rounded pieces the fragments of the former are rough and 
angular, with one or more faces planed smooth. 

Glacial rock waste or detritus has been deposited in 
various forms. Much of it has been spread over the sur- 



WORK OF AVALANCHES AND GLACIERS 101 



.^v. 



face as an imperfectly mixed mass of clay, sand, and gravel. 
These deposits are the well-known till plains of northern 
Europe and the United States. Not infrequently the 
material occurs in rounded hillocks or drumlins, or per- 
haps in long 
ridge -shaped 
bars, called 
eskers. The 
former are very 
common in the 
New England 
Plateau, the 
northern lake 
region, and 
also in Eng- 
land and Scot- 
land. Several 
of the islands 
in Boston har- 
bor are drum- 
lins. 

Near the 
southern limit 
of the glacial 
ice -sheet the 
drift occasion- 
ally takes the 
form of long 
ridges — perhaps many miles in extent, and one hundred 
feet or more in height. In nearly every instance these 
heaps are moraines. A part of Long Island is probably 
a terminal moraine, and several of the ridges that cross 
New Jersey are of similar origin. Many of the low ridges 
extending into the valleys of Colorado are moraines. 




SPLIT ROCK : AN ERRATIC BOWLDER 
The butternut-tree, growing from the cliff, is forty years old. 



162 PHYSICAL GEOGRAPHY 

A remarkable form of drift is found in the rounded 
blocks of stone strewn over the surface of the New England 
and Middle Atlantic States and a few other localities. 
These are commonly known as erratic boivlders. With re- 
spect to mineral character the bowlders are of many kinds; 
those of the northeastern United States are mainly of 
granite. The most interesting feature about them is 
the fact that they are unlike the rock in the locality 
where they are found; in some instances they certainly 
have been brought from a long distance. Some of them 
are of enormous size ; one, Split Bock, 10 near Mount Ver- 
non, New York, weighs not far from five hundred tons. 

Icebergs. — The formation of icebergs along the sea- 
front of glaciers becomes an important factor in several 
ways. The icebergs from the west coast of Greenland float 
southward during late spring, and during May and June 
cross the routes of trans-atlantic steamships, thus becom- 
ing a menace to navigation. Sometimes several hundred 
of them are drifting about in the vicinity of the New- 
foundland Banks, and remain there until they melt or are 
broken up by storms. The huge blocks broken from the 
Antarctic ice-sheet drift about over a very large area, some- 
times being found as far north as latitude 40° S. In the 
North Pacific Ocean the icebergs are small and are rarely 
found beyond the partly enclosed waters of the Alaskan 
coast and Bering Sea. 

QUESTIONS AND EXERCISES.— Describe any effects you have 
noticed with relation to snowslides on the roofs of buildings or steep 
slopes. 

A mass of snow weighing ten thousand tons moves with a velocity 
of twenty-five feet per second ; what is its momentum in foot- 
pounds ? Would this force be sufficient to break off or uproot large 
trees ? 

In a previous paragraph it is stated that the water issuing from the 
end of a glacier is muddy ; account for the presence of the mud. 






WORK OF AVALANCHES AND GLACIERS 1G3 

Explain the way in which rock fragments may get to the bottom of a 
glacier. Why are the scratches made by these fragments parallel ? 

Why are there no glaciers in the Appalachian Mountains ? 

The map on p. 157 shows the terminal moraine of the great ice-sheet ; 
describe its course and location. Name two large lakes situated in the 
basin of former Lake Agassiz. 

Describe any evidence of glaciation in the neighborhood in which you 
live, noting drumlins, eskers, moraines, markings and scratches, erratic 
bowlders, or drift. If possible delineate them on a map. 

COLLATERAL READING AND REFERENCE. 

Tyndall. — Forms of Water. 

Tyndall. — Hours of Exercise in the Alps. 

Le Conte. — Elements of Geology, pp. 569-583. 

NOTES. 

1 It is rare that snow accumulates to a depth of more than ten 
or twelve feet on a level area. On mountain slopes the snow is 
not evenly distributed, most of it finally lodging in ravines and 
places not exposed to the sweep of the wind. In laying the foun- 
dations for the observatory at the summit of Mont Blanc, the 
snow and ice were so deep that no rock bottom could be found at 
a depth of sixty feet. On the western slope of the Sierra Nevada 
Mountains the fall of snow sometimes reaches twenty feet on 
the level, while the drift may be several times as great. 

a Wet clothing hung out to dry in very cold weather first 
freezes and then gradually dries. An inspection of Table III., 
Appendix, shows that at a temperature of —40° F. a small amount 
of moisture may still exist in the atmosphere. 

3 The power of wind in drifting loose soil has already been 
noted. But snow is less than one-quarter as heavy as soil of 
average material ; hence the work of wind is far more effective. 

4 In certain parts of the Rocky, Cascade, and Sierra Nevada 
Mountains avalanches are of frequent occurrence, but they are 
by no means so common as in the Alps. In the latter ranges the 
slopes are steeper and the snowfall is considerably greater. It is 
not improbable that such snow-slides are just as common and 
quite as destructive in the Caucasus and the Himalaya Moun- 
tains as they are in the Alps. 



104 PHYSICAL GEOGRAPHY 

6 These are the poiulr eases (powdery snow), and they are the 
most dreaded of all snowslides. Damp snow does not shear and 
move readily ; it is the gathering ot light, dry snow, little by 
little, until finally the whole mass is in motion, that is the dis- 
tinctive feature of this form of avalanche. 

This form is known as the avalanche de fond. It is rarely 
destructive. 

7 The bands are alternate layers of ice and dirty snow. The ice 
is formed of snow that has been subjected to great pressure. Be- 
cause of the pressure all the air has been squeezed out, and for 
this reason the ice is tolerably clear and blue. The bands of snow 
contain air and are therefore whitish and opaque. 

8 The ice hummocks are conical in shape and, if present, are 
found almost always at the lower end. Not infrequently one of 
these hummocks is surmounted by a bowlder of several tons 
weight. The bowlder protects its support from the heat of the 
sun, while the latter melts the ice around the lower end of the 
column. Sooner or later the ice column breaks and the bowlder 
falls to a lower level, where the same process is again repeated. 

9 This peculiar feature at one time gave rise to the opinion that 
there might be an up-stream motion to a glacier. The reason for 
their direction, however, is evident ; the crack or break is neces- 
sarily at right angles to the direction of the strain. Now the 
movement of the ice is twofold — down stream and away from the 
bank. Therefore when the ice breaks the crack points diagonally 
up the stream. 

10 Many years since this bowlder broke into two parts along a 
cleavage plane. A butternut-tree sprang up in the cleft and in 
time its trunk has wedged the two fragments apart in the form 
of a V-shaped opening. In the northern part of Westchester 
County a large erratic block has been deposited on the top of 
three smaller stones, the latter forming a very firm tripod. In a 
number of instances one bowlder has been deposited on the top 
of a boss of rock in such a position that the equilibrium, while 
more or less unstable, cannot be readily overthrown. Examples 
are found throughout the New England Slates, and they are pop- 
ularly known as rocking stones. There is a fine example in 
Bronx Park, New York Oity. Hocking stones are also common 
in the glaciated regions of northern Europe. 



CHAPTER X 

THE WASTING OF THE LAND: THE RESULTS OF 

IMPERFECT AND OBSTRUCTED DRAINAGE. LAKES 

AND MARSHES 

In flowing from higher to lower levels along lines of 
least resistance, the water may find its passage temporarily 
obstructed, or perhaps wholly blocked by obstacles. 
Sometimes a ridge of land prevents its progress ; in other 
cases a landslide or, perhaps, a stream of lava athwart 
the channel prevents its progress. The water therefore 
spreads out, forming a lake, 1 pond, or marsh. In places 
where the flow is obstructed, one of two things must occur 
— either the water will collect until its surface is high 
enough to flow over the lowest part of the rim, or else it 
will spread over the surface until the amount that evapo- 
rates just equals that which flows in. The area whose 
waters flow into the lake constitutes its basin. A large 
basin usually has several rivers and many small streams 
that are its tributaries or feeders. 

Marsh Lakes. — In a region of considerable rain-fall, if 
the general slope be very decided, perhaps there may be no 
lakes and ponds, for the reason that the water flows oft', 
meeting no obstructions which cause it to collect in basins. 2 
On the contrary, if the surface be flat, the water, finding 
no definite channels, spreads over the surface and forms a 
multitude of small ponds. In Florida and along the Gulf 
Coast there are excellent examples, and they are commonly 
called marsh lakes. 3 

165 



166 



PHYSICAL GEOGRAPHY 



A marsh lake of large size or considerable depth could 
not form in perfectly flat lands, for the reason that, after 
reaching a certain height, the water would flow off as fast 
as it was supplied. For a similar reason, such lakes could 
not be very numerous on a surface that had a consider- 
able slope. 4 But while many — perhaps most— of the 
lakes have been formed by the surplus of rainfall over 
drainage, there are many thousand lakes that are the 
result of factors with which rain-fall has no direct con- 




MARSH LAKES, FLORIDA. 



nection. The most important are those whose basins have 
been shaped largely by the action of moving streams of 
ice — that is, by glaciers. 

Glacial Lakes. — A glance at a good map of the north- 
ern part of North America shows that the lakes of this 
region are its most remarkable surface feature. As a rule 
they are long and narrow, and if a group of them be con- 
sidered, it is at once apparent that their axes, or lines of 
greatest length, are nearly parallel. Careful investigations 



IMPERFECT AND OBSTRUCTED DRAINAGE 107 

have shown that not only are such lakes comparatively 
much deeper than the marsh lakes previously described, 
tmt that also, in most instances, their basins have been 
wrought in the hardest rocks. In many instances, too, 
their rims are walls of bowlders that could scarcely have 
been more regular, had the courses of rock been laid by 
human hands. 5 

Very frequently such lakes occur in chains, a river fol- 
lowing the course of each chain ; indeed, these lakes are 




GLACIAL LAKES 
A group in the Adirondack Mountains, New York. 

merely incidents in the history of the river. In a few 
instances a cluster of such lakes apparently radiates from 
a central point, as is seen in the " linger" lakes of New- 
York. Lakes of this type are closely associated with the 
great accumulation of glacial ice fi that formerly covered a 
large part of the northern hemisphere. The lakes them- 
selves are found in glaciated regions only — never else- 
where. They are therefore called glacial lakes or, in the 
British Isles, tarns. 



168 



PHYSICAL GEOGRAPHY 



Accidental Lakes. — There are other lakes whose 
origin is the result of accident ; such as the destruction 
of a river loop, the damming of a stream, 7 the formation 
of a bar across an estuary or cove, or the sinking of an 
(area of land. Very many lakes have come suddenly into 
existence through one or another of the causes named. 

In the illustrations pp. 110 and 173 there is shown a 
type of lake that is common along the bottom lands of the 
Mississippi and other rivers that flow through level plains. 
The origin of such lakes is very apparent. The lakes 
themselves are manifestly the abandoned loops of rivers, 
and they are formed when the river straightens its channel. 
The moat thus formed remains filled with water. Perhaps 
a bayou or small stream may be left as a feeder, but more 
likely the moat becomes a stagnant pool, sooner or later 
to disappear — possibly overgrown by vegetation, possibly 
buried under the sediment brought down by floods. 

Another type of accidental lake occurs along low, flat 
coasts. These are the lagoons of the sea-shore or the lake- 

shore. The 
south coast of 
Marthas Vine- 
yard furnishes 
an excellent il- 
lustration of la- 
goons of this 
type. In times 
past, this shore 
was a succes- 
sion of coves 
and small bays. 
But the water 
on this side of the island is so shallow that the waves, 
dragging heavily on the bottom, have pushed enough sand 




LAGOONS, MARTHAS VINEYARD 



IMPERFECT AND OBSTRUCTED DRAINAGE 169 

before tliem to throw barriers across the coves, and shut 
them off from the ocean. 8 

Any good map of the United States or of Europe will 
show a multitude of wave-formed lagoons of this character. 
Those near the shore often have more the nature of sounds 
than of lagoons. 9 But as the coast, little by little, extends 
seaward, many of them now near the shore will ulti- 
mately be at a considerable distance inland. 

Salt Lakes. — Salt lakes have no outlets, and for that 
reason they are salt. 10 Nearly all soil contains more or 
less mineral salts that are soluble in water. Even the 
hardest granites and igneous rocks contain a minute pro- 
portion of soluble matter. So when the water flows to 
the basin, it carries with it any soluble matter with which 
it comes in contact. If the lake or pond has an outlet, 
both the water and the salt flow off together. 11 If there 
be no outlet, however, the water is removed by evapora- 
tion, while the mineral salts, which cannot evaporate, 
remain in the basin. In time, the water becomes decid- 
edly salt, and finally, a brine that will dissolve nothing 
more. After this, unless there is an inflow of fresh water, 
the salt sinks to the bottom, and forms also a wide mar- 
gin of crusted salt along the shore. 

Temperature and atmospheric moisture are also factors 
in the origin of salt lakes. High temperature and dry- 
ness of the atmosphere both promote evaporation, and 
doubtless there are regions, whose lakes are now fresh, 
that would become regions of salt lakes were the tem- 
perature and dryness to increase materially. 

Although salt lakes have no outlets, it is not necessarily 
true that lakes without outlets are salt. As a matter of 
fact, there are many such lakes whose waters are almost 
as sweet and pure as when they fell from the clouds. Of 
this apparent contradiction there are two explanations. 



170 PHYSICAL GEOGRAPHY 

In the first place the lakes may be young. In this case, 
time only is required to change the fresh lake to one of 
brine, and the time will be long or short, according as 
the soil through which the feeders flow contains little or 
much soluble matter. In the Great Basin, west of the 
Rocky Mountains, there are several young lakes, whose 
waters are comparatively fresh, 1 ' situated almost alongside 
lakes of briny saltuess. In the second place, all the 
soluble matter may have been leached from the soil at 
some prior time when the lake overflowed its basin. 
There are many such lakes in Canada and the United 
States. They are not salt, and unless their conditions of 
existence are changed they will not become salt. 

There are certain lakes, mainly in arid regions, that are 
periodic in character. During the rainy season they may 
be of considerable size ; they have no great depth, how- 
ever, and in the dry season their waters evaporate, leaving 
in each basin a thick crust of salt. There are numerous 
small lakes of this character in the western part of the 
United States; some of those in southern Russia are of 
considerable area. Lakes of this kind are commonly called 
play a lakes. Commercially some of them are important 
on account of the enormous amount of salt the} r yield. 

Physiographic Aspect of Lakes. — Lakes are the most 
transitory features of the earth's surface. Rivers and the 
various relief features of the earth are seldom entirely 
obliterated ; but as time is reckoned a lake is the creation 
of a very brief period. Its life is almost ephemeral, and 
various forces are constantly at work to destroy it. Physi- 
ographic agents that have no effect on other features of 
the earth are often fatal to the existence of lakes. 

Among the various agents, glaciers are, perhaps, the 
chief. Glaciers have been energetic factors in making 
lakes, it is true ; they have also been quite as effective in 



IMPERFECT AND OBSTRUCTED DRAINAGE 171 

causing their destruction. The glacier blocks the channel 
of a river with ice or with gravel, and in a short time a lake 
is formed. Later it forces a passage through the obstruc- 
tions made, and in a little while the lake has disappeared. 13 
A few old shore marks and, perhaps, a delta or two are all 
that remain to tell the story. 




A BURIHD LAKE BASIN 
The b.isiu lias been filled with sediments brought into it by the river. 

A change in the level of the lake-bed by elevation or by 
depression always produces great changes in the lake. Such 
a change may throw up a ridge so as to form a basin for a 
new lake, but it may also lower the land at the foot of the 
lake and destroy the basin of an old one. Long before the 
existence of the lakes whose remnants are now found in 
the Great Basin, a vast body of water covered much of 



172 PHYSICAL GEOGRAPHY 

this region. But a change in the level of the basin 
occurred, and this, together with probable changes in 
climate, caused the great internal seas gradually to dis- 
appear. 14 

Rapidly growing vegetation is also a potent factor in 
the destruction of lakes. Vegetation has but little effect 
on deep lakes, but in the case of marsh lakes it has a great 
deal. The process is very simple : the roots, stalks, and 
leaves of the dead plants fill the basin until there is no 
more room for the lodgement of water. Usually the plant 
begins its growth at the edge of the lake and spreads 
toward the centre, gradually filling the basin, until a deep 
hole is all that remains. The struggle of the lake may be 
a long one, but in the end the vegetation conquers. Buried 
and partly obliterated lakes of this character are common 
in all coast plains and level lands. One near Goshen, 
New York, covering an area of about sixty square miles, 
has disappeared within recent times and most of its former 
bed is now cultivated land — the famous "onion fields" of 
the State. 

Winds are sometimes very effective in the destruction 
of lakes, especially the lagoons along the seashore. The 
manner in which they operate is very simple ; they merely 
carry enough fine rock waste into the basin to fill it. 15 
The rock waste is piled upon the windward shore, and 
the latter advances, little by little, until finally it meets 
the opposite shore. The lagoon is filled, and at the 
same time an estuary becomes a part of the coast plain. 
Such instances are common on coasts that are swept by 
constant winds. 

The foregoing are the most apparent agencies that con- 
tribute to the destruction of lakes ; and although in many 
instances they operate continuously and systematically, 
they are confined to localities of comparatively small area. 



IMPERFECT AND OBSTRUCTED DRAINAGE 173 



But there are other lake-destroying agencies whose opera- 
tions are carried on in almost every part of the earth ; 
their manner may not be quite so apparent, but it is none 
the less effective. " Rivers are the mortal enemies of 
lakes." * The stream that flows into a lake bears in its 
volume more or less silt, which is promptly deposited in 
the lake basin, lit- 
tle by little filling 
it. With scarcely 
an exception, at 
the place where a 
stream enters a 
lake, either a del- 
ta or a bar is 
formed. This is 
clearly illustrated 
by the Volga, Avith 
its mazy delta ; 
by the St. Louis, 
at the head of 
Lake Superior ; 

and by St. Clair River, at the head of Lake St. Clair, and 
in the lakes of central New York. 

The stream that flows out of the lake is equally destruc- 
tive. It cuts away the rim of the basin, lowering the level 
of the lake until the water is nearly or quite drained. Not 
a few of the lakes that have disappeared from the earth 
have been destroyed in this manner. 

A diminution in the rainfall sooner or later will also 
destroy a lake. The lakes and old lake-beds in the Great 
Basin illustrate this fact. Formerly Great Salt Lake and 
its scattered remnants — the latter, many of them, now dry 
— covered an area almost half the size of Lake Superior. 

* Gilbert. 




LAKE ST. CLAIR. 

The mud flats at the head of the lake are the result of sedi- 
mentation. 



174 



PHYSICAL GEOGRAPHY 



'.'I.v,:v:D:v:: : :'A:-:v^H 




Former Lake 
:. . :.; Dry Land 
nts of former Lake -j 



LAKE BONNEVILLE AND ITS REMNANTS 

The area in white shows the former si^e of the lake ; the small 
lakes south of Sevier H{iver are practically dry. 



At that time the 
level of the lake 
was nearly one 
thousand feet 
higher than at 
present. After- 
wards, however, 
the rainfall de- 
creased and, the 
indraught being 
less than the 
loss by evapor- 
ation, the lake 
dwindled to its 
present size. 

In almost 
every part of 
the world are 
found old lake 
shore-lines high 
above the sur- 
face whose level 
they formerly 
marked. 16 In 
some instances 
they surround 
the sites of 
lakes that have 
ceased to ex- 
ist ; in others, 
of lakes that are 
reaching a pe- 
riod of old age. 
In any case 



IMPERFECT AND OBSTRUCTED DRAINAGE 175 

they serve to demonstrate that lakes are very transit- 
ory. 

Many of the lakes of the United States have disap- 
peared within very recent times. Sevier Lake in Utah 
has practically ceased to exist, and Tulare Lake, California, 
in twenty years has shrunk to less than half its former 
size. The finger lakes of New York have lost a measur- 
able part of their area in the past fifty years, and the level 
of the Great Lakes has been materially lowered. In Lake 
Erie the diminution has interfered so much with navi- 
gation that a barrier across the outlet is now contem- 
plated in order to raise the level of the lake. 

Geographical Distribution of Lakes. — Lakes occur 
in all parts of the earth, but they are by no means uni- 
formly distributed ; as a matter of fact about ninety 
per cent, of them are north of the 40th parallel of north 
latitude. 

With respect to glacial lakes this law holds almost 
universally true. The only exceptions are the few that 
are found in the southern Andes and the snow-clad sum- 
mits of high plateaus and mountains. Most of them 
are situated in Europe and North America. In the lat- 
ter division alone there are more than one hundred 
thousand glacial lakes. Why are the latter of rare occur- 
rence in the torrid zone ? Where in this zone would they 
occur ? 

Salt lakes are confined mainly to regions of deficient 
rainfall. 17 Why are they not common in regions of abun- 
dant rainfall ? Most of them occur in the basin regions of 
North America and Eurasia ; in the latter region there are 
several thousand. The Caspian " Sea," the largest lake in 
the world, is in this region ; its surface is eighty-four feet 
below sea-level. Playa lakes are numerous in regions 
having a level surface and a light, periodic rainfall. 



176 



PHYSICAL GEOGRAPHY 




Most of the lakes may be 
grouped in systems which 
occupy lines of depression 
on the earth's surface. Two 
such systems are found in 
the Western and three in the 
Eastern Continent. The 
lakes of the Western Conti- 
nent are chiefly in North 
America, and are embraced 
mainly in two systems. The 
largest and most important 
is the belt stretching across 
the northern part of North 
America. An arc of a great 
circle drawn from the city 
of Buffalo to Point Barrow 
passes through or near a 
chain of lakes that includes 
about the largest bodies of 
fresh water in the Avorld. 
Find this chain on the map ; 
describe the drainage and 
character of the lakes. An- 
other system extends from 
the northern boundary of 
the United States southward 
through Mexico and the 
Central American States. 
Most of these are situated 
in a basin region ; describe 
their drainage and character. 

South America is remark- 
able for the absence of lakes 



IMPERFECT AND OBSTRUCTED DRAINAGE 177 

iu any considerable number. There are playa lakes along 
the eastern base of the Andes, but the only lake of impor- 
tance is Titicaca, 18 a large body of water near the summit 
of the Andes. Its surface is 13,000 feet above sea-level, 
and it is the highest large lake in the world. Do its waters 
reach the ocean ? 

In the eastern continent a wide belt of lakes, situated 
mainly between the 50th and 60th parallels, extends across 
Eurasia ; what is their character ? With respect to lati- 
tude their position corresponds pretty closely to that of 
the glacial lakes of North America. These lakes constitute 
the great majority in number, but they are of very little 
importance. 

A second belt follows the high mountain-ranges that 
stretch from west to east across the continent. It em- 
braces the pla} r a lakes south of the Atlas Mountains ; the 
glacial lake of the Alpine and Himalayan folds ; and the 
multitude of playa and salt lakes in the basin region. 
Many of the largest and most of the important lakes of the 
continent are in this group. A third system in Africa 
follows the line of the eastern highlands, and therefore, 
unlike the other sjstems, extends north and south. 
Next to those of North America the African lakes are the 
largest bodies of fresh water in the world. Name and de- 
scribe the four largest. 

In one respect the Australian lakes are remarkable — 
almost every one is either a playa or a salt lake. Not a 
single one of any importance has an outlet to the sea. 
What does this indicate with reference to the rainfall of 
the continent ? 

Swamps and Marshes. — In some places the drainage 
waters cannot flow off, but remain about even with the 
surface, thereby forming what are variously termed 
siram/ts, morasses, pocosous, !><»/*, and marshes.™ 



178 PHYSICAL GEOGEAPHY 

Inasmuch as almost every condition of imperfect or 
embarrassed drainage results in marshy ground, it is evi- 
dent that many different factors -may bring about such 
conditions. For instance, the surface of the land may be 
so nearly a perfect level that the water cannot run off 
until it has completely saturated the soil. Such instances 
are very common : they occur in prairies and the flood 
plains of rivers almost without number. They are com- 
monly, though not always properly, called river terrace 
swamps. Quite as frequently such morasses form at the 
mouths of rivers, where they form delta swamps, or estuary 
sivamps. 

In many instances the accumulation of vegetable matter 
results in swamps. Under ordinary conditions the leaves 
and twigs of forest growths quickly decay if they fall on 
dry ground and, as a rule, the products of decay are 
gaseous. Under such circumstances, therefore, no great 
amount of solid matter results from such decay. But if 
the ground be tolerably wet and rainfalls are frequent, 
there may be enough moisture to prevent complete decay. 
The vegetable matter gradually acquires a well-known 
condition, in which it consists of a fine, black slime and a 
mass of fibrous material called peat. 21 The accumulated 
matter prevents drainage and a swamp finally results. 
Most woodland sivamps are formed in this way. 

Not all woodlands become swamps, however, for the 
character of the vegetation nearly always has more or less 
to do in swamp-making. Several species of sphagnum, a 
kind of moss, are intimately connected with swamps. One 
of these water-mosses consists of very long, thread-like 
stems which, while dead at one end, are living and grow- 
ing at the other. The dead portions do not decay, how- 
ever ; they simply accumulate, packing tightly together 
like an immense mass of sponge. 



IMPERFECT AND OBSTRUCTED DRAINAGE 179 

So, if the ground ever becomes wet enough for the 
water-loving sphagnum to get possession, the area will 
become a swamp, even if the accumulations of other vege- 
table material would not result that way. In time a 
hollow, a pond, or even a marsh lake will be entirely filled 




EFFECTS OF VEGETATION 
Swamp vegetation beginning at the shore, are extending outwards. 

with the stems of sphagnum, thus forming peat bogs and 
lacustrine swamps? 2 

If sphagnum once obtains in an area, an absolutely 
level surface is not necessary for the formation of swamps. 
The sphagnum will make its way up a slope of four or 
five degrees and thus form a climbing bog. Instances of 
this kind are common in the Scandinavian Peninsula and 
also in Nova Scotia and the New England States. 




llSiSIsS ! ^^s^^^^^s^^^^SM^ 



EFFECTS OF VEGETATION 

Swamp grasses and sphagnum have nearly piled the lake, and a quaking bog ts beginning 

to form. 

Sphaguous growths not ouly overwhelm shallow ponds 
and lakes, by filling their baskis from top to bottom, but 
sometimes they operate against deeper waters. If the moss 
stems cannot find lodgement at the bottom of the lake they 
will float at the surface, spreading, little by little, until the 
surface is covered. The mat of sphagnum grows thicker 



180 PHYSICAL GEOGRAPHY 

and broader, and is made firmer by pasty matter, that 
results from partial decomposition. In time the surface 
becomes firm enough to serve as the bed of a wagon road, 
or even a railway. But the surface never gets quite firm, 
and when one jumps upon it, or drives a wagon over it, the 
shaking is always perceptible. In this manner a marsh 
lake is changed to a quaking bog, 23 or prairie tremblante. 

There are other species of vegetation 2i that have more 
or less to do with swamp formation — among them cane- 
brakes. Canebrakes have long been associated with 
swamps, but usually as a result. As a matter of fact, 
canebrakes are not infrequently a cause of swamps. The 
roots of the plant, spread out just below the surface of the 
ground in much the same manner as does the sphagnum 
above ground, making finally a mat that almost wholly 
obstructs drainage. 

Coast or salt marshes are confined to low coast plains. 
They are destitute of water mosses, but they contain other 
species of vegetation that are quite as effective. The first 
step in the formation of a salt marsh is an area of shallow, 
still water. Usually this results as soon as a sand-bar is 
thrown across a cove or estuary. Waves prevent the 
development of marine swamp, but in throwing up a bar 
they make the condition that is a foundation for the 
swamp. In a few instances sheltering headlands keep the 
water still enough for the growth of marine plants. 

The next stage is the growth of eel grass, a plant with a 
long, slender blade. This takes root as soon as the cove 
begins to fill with sediment ; it grows rapidly, and the 
half-decayed remains contribute not a little in filling up 
the marsh. But eel grass grows only when covered with 
salt water, and when the decayed vegetation, mixed with 
wind-blown rock waste, has filled the cove to low-tide 
level, it perishes. After a time the marsh passes a step 



1MPEKFECT AND OBSTRUCTED DKAINAGE 181 

higher in its formation, receiving layer after layer of sedi- 
ment that build its surface to a level where it is awash at 
high tide only. 

By this time true salt-marsh grasses, reeds, rushes, and 
tides obtain possession. These species thrive only when 
their roots are covered with salt water at short intervals. 
They accumulate until the level of the marsh is built 
above the level of the highest tides. When this stage is 
reached turf grasses gradually take the place of salt-marsh 
grasses, and the marsh becomes meadow land. 

Another plant active in swamp-making is the mangrove- 
tree. This tree thrives only in salt water. It propagates 
itself partly by upshoots from the enormous mass of roots 
that trail under water, and partly by seeds. The growth 
and spreading of mangrove roots and trunks is so great 
that coast outlines are extended rapidly and fringing bur- 
ners are formed as well. In Florida mangroves and corals 
are yearly adding measurably to the swamp-land surface 
of the State. 

The tundras of the Arctic coast plain furnish an inter- 
esting example of the combined action of ice, fresh water, 
salt water, and moss. These shores are almost constantly 
covered with ice. Not only are they inundated by tidal 
waters, but also by stream waters. The mouths of the 
streams are frozen, and the flood water, finding its chan- 
nels blocked with ice, spreads broadcast over the surface. 

During flood seasons the stream waters are filled with 
sediment, and this is spread over the plain. Moreover, it 
furnishes sufficient nutriment to heavy growths of coarse 
moss, and the latter, in turn, not only holds the sediment 
in place, but it also in no small degree prevents the melt- 
ing of the ice. As a result, this plain is a perpetually half- 
frozen morass, and probably the most inhospitable region 
on the face of the earth. 



182 PHYSICAL GEOGRAPHY 

Physiographic Aspects of Marshes. — Notwithstand- 
ing the fact that the area of marshes and swamp is com- 
paratively small, it is probable that much of the land sur- 
face of the earth has been a marsh or a swamp in some 
period of its existence. In a way marine marshes may be 
considered as land at an intermediate stage between sub- 
mergence and elevation. Hence, volcanic areas excepted, 
the shallow lagoon, the eel grass swamp, the barren mud 
flat, the salt grass marsh, and the turf-covered plain is 
each, in turn, an incident in the final elevation of a body of 
land above sea-level. 

Along the coast of the South Atlantic States one may 
find the lagoons and the eel grass swamps ; along the 
shores of the Gulf there are, in addition, very broad mud- 
flats; 25 in the bay of San Francisco and the adjacent 
waters are many square miles of salt-grass and tule 
marshes ; and almost everywhere beyond the reach of tidal 
waters there are the turf-covered plains. 

The range of fresh-water swamps may not be quite so 
great, but economically they are quite as important as the 
marine marshes. Their evolution and physiography, 
moreover, is rather more complex than the development 
of marine marshes, but in two respects they are alike — 
namely, vegetation makes them and, in the long run, it de- 
stroys them. 

Vegetation may, and usually does, operate to create 
swampy conditions, but the process of destruction does 
not differ from that of creation. The accumulation pro- 
ceeds until the surface is lifted to a level where the ground 
waters may flow off. 

Cultivation destroys swamps, and the process of destruc- 
tion is simple. Most grains and food-stuffs require a com- 
paratively dry soil, and the very act of ploughing creates 
drainage channels in which the water flows off. Where 



IMPERFECT AND OBSTRUCTED DRAINAGE 183 

ploughing lias not been sufficient, ditching and under- 
draining accomplish the same results. 

But SAvamps themselves exert not a little influence on 
vegetation and its distribution. Many species of tree and 
shrub that thrive in moist or dry soils perish if the soil be 
saturated. Thus, a swamp once obtaining in a woodland 
area, it is a question of time only before many, possibly 
all of the forest species disappear. In almost every fresh- 
water swamp the most marked features are the stumps 
and trunks of dead trees — a result of the development of 
swampy conditions. What species of evergreen thrives in 
swampy lands ? 

Economic Value of Swamps. — Swamp, marshes, and 
bogs, although practically uninhabitable for human beings, 
have had a very far-reaching effect in the development of 
civilization. In evidence of this the results of the coal-beds 
may be cited. The enormous development of commerce 
and manufactures is due almost wholly to the coal-fields of 
the world, and these almost without exception are the 
swamps and marshes of prior geological ages. 

The swamps of the present time are the most productive 
areas to be drawn upon in the future. The soil possesses 
great depth, and its nutrient qualities are exceedingly 
great. Swampland crops themselves are of no little im- 
portance, and the rice-swamps probably supply food to a 
greater number of people than all the other grain-fields in 
the world. Incidentally, the world's supply of cranberries 
comes mainly from swamps, and the peat-bogs furnish fuel 
to not far from fifty millions of people. 

The Movement of Rock Waste. — In this and the 
preceding chapters it has been shown that the higher parts 
of the land are almost everywhere crumbling and wasting 
away under the action of water in one or another of its 
different forms. Rain, snow, ice, running streams, and 



184 PHYSICAL GEOGRAPHY 

even the winds are factors that are unceasingly active, and 
their legitimate work is to wear away the land and trans- 
port the material removed to sea-level. 

On the steeper slopes, as a rule, the rock waste is coarse, 
the fragments sometimes weighing many tons. On its 
way downward it is broken and worn in various ways 
until, at sea-level, it is very fine. Much of it is also min- 
gled with the remains of vegetation, and takes the charac- 
ter called soil. 

The soil is deposited in river valleys in the form of flood 
plains, delta plains, estuary plains, and coast plains. Re- 
view briefly the formation of each. Some of it is arrested 
by obstructions along its downward journey and, filling the 
depressions in front of the barriers, forms lacustrine plains. 
Name several examples. Explain how all these physio- 
graphic processes affect the habitability of a region. 

The waste of the old land is the material of the new. 

QUESTIONS AND EXERCISES.— Study any lake or pond near 
which you live and classify it as marsh, glacial, swamp hole, or salt ; 
make a map of it. 

Note whether a coast plain is present, or whether the water-level is 
at the foot of cliffs or banks. 

If there is a fringe or belt of coast plain what does it indicate con- 
cerning the present and the former size of the lake ? 

Note whether or not the border is marshy and thickly covered with 
vegetation, or whether it is strewn with large bowlders. 

In what, if any, part are the waters muddy ? From this determina- 
tion endeavor to find where the sediment is chiefly deposited. 

From the foregoing write a description of the body of water. 

From the diagram of the Great Lakes, together with a good map, 
p. 176, prepare a description of these lakes. What will be the effect 
of the recently completed ship canal at Chicago, on the level of Lake 
Michigan ? 

What would be the effect on the character of the water were the 
basin of the Caspian Sea to fill until it overflowed ? 

If the basin of the Black Sea were elevated twenty or thirty feet 
what would the water be, salt or fresh ? 



IMPERFECT AND OBSTRUCTED DRAINAGE 185 

Mention some of the benefits resulting from the Great Lakes of North 
America, with reference to commerce, industries, and climate. 

Which of the two Great Lakes may be regarded as a single body of 
water ? Why ? 

The level reach of land in the illustration, p. 171, was formerly a 
lake ; explain how it became the flood plain of a mountain stream. 

From any convenient source of reference write a description of Death 
Valley, California, or of the Dead Sea, Syria. 

From the section of the marsh lakes, p. 166, prepare a description 
of them, concerning their depth, altitude, and navigability. 

COLLATERAL READING AND REFERENCE. 

Russell. — Lakes of Nevada, Physiography of the United States, 
pp. 101-130. 

Le Conte. — Elements of Geology, pp. 80-82, 580-581. 
Shaler.— U. S. Geol. Survey, An. Rep't, 1800. 

NOTES. 

1 There is no distinction between a lake and a pond, except the 
very indefinite one of size. 

" Lakes are sometimes formed, however, in places where a steep 
slope joins one that is very moderate. Examples of such lakes 
occur in the eastern slope of the Scandinavian Peninsula and in 
Nevada. 

3 Marsh lakes are rarely more than a few feet in depth. They 
are seldom navigable, and commercially they are of but little 
importance. In Europe many such lakes have been drained in 
order to make cultivable land of their beds. There are several 
instances where such basins are filled with water and used for fish 
culture for a period of several years, and then drained and culti- 
vated for a like period. 

* Occasionally lakes are formed on mountain-slopes by the 
agency of landslips, but they are seldom long lived. Sometimes 
they break through the material that blocks their jverflow, but 
more commonly the outflowing water cuts a channel through it 
deep enough to drain the lake to the bottom. 

""Walled" lakes are common in Iowa, Minnesota, and Da- 
kota. So regular are the walls of their shores that for many 



186 PHYSICAL GEOGRAPHY 

years it was commonly believed they were artificial and were 
built by a prehistoric race of people. As a matter of fact, how- 
ever, the walls are the work of ice. In severe winters these lakes 
freeze nearly to the bottom ; but inasmuch as water increases in 
bulk when it freezes, the ice, in expanding, pushed the bowlders 
shoreward. Time and time again this process was repeated until 
the rocks were pushed back to a position where the resistance of 
the earth back of them was equal to the pushing force of the ice. 
" In scraping out these basins not the ice itself, but the frag- 
ments of rock held at the bottom, form the cutting tool. 

I There are several instances in which flowing lava has blocked 
up a river channel and formed a lake. In at least two places the 
Columbia River was thus blocked, and the high-water marks of 
the lakes formed are still plainly visible. In each instance, how- 
ever, the river succeeded in recovering its channel and the lakes 
were therefore drained. Accidental lakes, resulting from the 
blocking of a river channel by coulees of lava, are common in 
volcanic countries. Still another accidental lake is the crater 
lake, which is merely an old volcanic crater filled with water. 
Crater Lake, in Oregon, and Lucrine Lake, in Italy, are exam- 
ples of such lakes. The former is about 2, 300 feet deep and is 
a wonderfully interesting body of water. 

8 Not only have coves of the sea-shore been shut off by bars, 
thus forming lagoons, but the same process has been carried on 
along the shores of lakes. Such lagoons are in process of 
formation at the head of Lake Superior, Lake Erie, and Lake 
Ontario. In each case, however, the formation of the lagoon is 
not yet complete, owing to the fact that the current from the 
river is still able to keep a channel open. 

a Albemarle and Pamlico Sounds are examples, and they re- 
main as sounds for the reason given in the preceding note. In 
other words the sound is often an intermediate stage between a 
bay and a lagoon. 

10 There are a few small salt lakes having outlets, but none of 
importance. They are saline because of salt springs within their 
basins. Not all so-called salt lakes contain common salt, how- 
ever ; in many various alkaline substances are found. 

II Near the City of Mexico formerly there were several lakes that 
overflowed into a fourth. The latter is salt, the others not drained 
are fresh. Utah Lake overflows into Great Salt Lake through 



IMPERFECT AND OBSTRUCTED DRAINAGE 187 

Jordan River ; its waters are fresh. Lake Chad, in Africa, is 
normally without an outlet. Occasionally, however, in seasons 
of unusual rains, it overflows into the Libyan Desert. This 
occasional overflow is sufficient to keep its waters fresh. The 
waters of the Caspian Sea are kept moderately fresh by a similar 
process. On its eastern border is a gulf, the Karabogas, con- 
nected with the main body of the lake by a narrow strait. The 
waters of the gulf are very shallow, and so great is the evapora- 
tion, that a four or five knot current is constantly flowing into 
it from the main body. From this inflow about 250,000 tons of 
salt are deposited daily. Now, if this amount of salt were left 
dissolved in the lake the latter would sooner or later become a 
saturated brine. But because of this separation and deposit of 
salt, the waters have not become perceptibly Salter, in the time 
since measurements have been made. 

12 It seems a contradiction of facts to assert that a salt lake 
may become fresh by a process of drying up ; nevertheless this 
has been the history of many lakes. During a long-continued 
period of deficient rainfall, a lake may dry up, leaving its mineral 
salts as a deposit upon the bottom. In time the winds cover 
this saline crust with a thick layer of fine soil ; and when the 
lake again begins to fill, its waters are fresh. Pyramid and Win- 
nemucca Lakes in Nevada are illustrations ; their waters are 
comparatively fresh. 

13 Lake Agassiz, a body of water considerably larger than the 
five great lakes, formerly covered a large part of the valley of the 
Eed River of the North. The destruction of this body of water 
was caused probably by glacial action. It had several outlets, 
one of which was the present channel of the Minnesota River. 

M This lake preceded any of the lakes now in the Basin Region, 
and was older even than the Uinta Mountains. The bed of the 
lake seems to have been lowered, and this, in part, was probably 
one factor in its destruction. 

14 It is not unlikely that Lake Mreris, in Egypt, was destroyed 
by winds. It was situated a few miles southwest of the Nile 
delta and disappeared within historic times ; but until within a 
few years its exact position was not known. In this region the 
movement of wind-blown rock waste is incessant, and the amount 
moved in even a few days is enormous. Former canals across 
the Isthmus of Suez, one after another have been filled by rock 



188 PHYSICAL GEOGRAPHY 

waste, and there is every appearance to suggest that the isthmus 
itself was formed largely through feolian agency. 

16 The old shore lines of Great Salt Lake are still a marked 
feature, and, excepting the few places where they have been 
obliterated, they have been surveyed throughout the entire cir- 
cuit of the lake. Old shore lines have' been found above the 
present level of Lakes Titicaca and Maracaibo, and also above 
the level of the lakes of the western part of the Great Basin. 
Two old shorelines of Lake Ontario have been found in New 
York, one of which, the "Ridge Road," may be traced along 
nearly the whole extent of the southern shore. In time its 
level has been somewhat warped and it has now a grade of one or 
two feet per mile. 

17 In many instances the carbonates of alkaline metals are pre- 
sent in such quantities that the waters of the lake are strongly 
alkaline. Many of the lakes of the Great Basin are alkaline. 

16 Lake Maracaibo is a lagoon or "clover-leaf" bay, rather 
than a lake of ordinary character. 

19 It is difficult to draw the line between marsh lakes and 
swamps on the one hand, and quite as difficult to distinguish 
between the latter and meadow lands on the other. The differ- 
ence is practically one of degree. A lake or a shallow lagoon 
passes through all the intervening stages. 

20 In many instances the emergence of underground waters to 
the surface, by percolation (see illustration, p. 133), causes 
swamps. The various bolsas on the coast plain between Los 
Angeles, California, and the ocean are formed in this manner. 

21 It is well to bear in mind that peat is not a plant, but a 
condition of imperfect decomposition that, under certain condi- 
tions, almost all vegetable tissue may assume. The softer and 
more soluble parts of the tissue are changed to a black slime 
popularly known as " mud," are really a mixture of nearly pure 
carbon and hydrocarbons ; the wood fibre remains. It is likely 
that the incorrect popular notion has arisen from the fact that 
nearly all the peat used for fuel is derived from species named. 

22 Although all lacustrine swamps are old lakes that have been 
destroyed by vegetation, not all of them become peat-bogs. In 
many instances the lake is situated north or south of the lati- 
tude in which sphagnum thrives. The peat-bogs of Ireland 
are historic, but they are not more extensive than those of the 



IMPERFECT AND OBSTRUCTED DRAINAGE 189 

Danube. They occur in nearly every country in which sphag- 
num grows. 

33 Quaking bogs are very common in the swamps of the South 
Atlantic States. Usually the mat of sphagnum spreads from the 
margin toward the centre, but in many instances patches of 
the plant accumulate in the open water, forming islands. 
Generally the insular patches are attached to the bottom, but not 
infrequently they float hither and thither. In time they spread 
marginally until the surface is finally covered. The mat of 
accumulated sphagnum receives more or less earthy matter and 
becomes a tolerably firm surface. In California one of the lines 
controlled by the Southern Pacific Company was built across a 
quaking bog a distance of several miles. It finally caved in, 
however, engulfing several cars of a freight train. 

34 The various species of rush, flag, reed, and sweet briar are 
associated with swamps and contribute not a little to their for- 
mation. The wild grape and several species of wild smilax are 
also abundant in swamps. These species, however, are found 
mainly south of the latitude in which sphagnum thrives. 

25 The mud-flat stage is always present; it is merely the area or 
belt that is uncovered at low tide. If the slope is gentle this 
belt may have considerable width — and this is the case along the 
coast of the South Atlantic States and the shores of the Gulf. 
Along shores swept by fairly high tides the mud-flat belt is 
usually wide. 



CHAPTEE XL- 
OCEAN WATEES AND THEIK MOVEMENTS: WAVES, 
TIDES, AND CURRENTS 

Almost all the phenomena connected with the wasting 
of the land, with climate, and with the existence of life, in 
one way or another, depend on the sea, whence comes all 
the waters of the land. In at least two ways the sea dif- 
fers from other bodies of water. It is many thousand 
times the size of the largest body of fresh water and, 
two or three inland lakes excepted, its surface level is 
lower. Practically it supplies the land with its fresh 
water, and because of its lower level, almost all the waters 
of the land are flowing back into the sea. 

Sea- water is briny and bitter ; doubtless it has always 
been thus, but, inasmuch as the stream waters flowing into 
it are constantly dissolving mineral matter from the rock 
waste and carrying it to the ocean, the amount in the latter 
is constantly increasing. Every one hundred pounds of 
sea-water, on an average, contains about three and one- 
half pounds of saline matter ; most of this is common salt, 
the remainder being chiefly lime and magnesia. The per- 
centage of mineral matter varies. In localities where 
evaporation is rapid, the proportion of salt is larger. 
Thus, in the Red Sea 1 it is more than four per cent., 
while in the Baltic Sea it is less than one-half as great. 
It is somewhat greater in tropical than in polar regions. 

Bulk for bulk, sea-water is heavier than fresh water. A 
cubic foot of fresh water weighs about 1,000 ounces ; on 

190 





■Ill 




ifej 








ml 




192 PHYSICAL GEOGKAPHY 

account of its mineral matter the same volume of sea- 
water weighs at least thirty-five ounces more. Tempera- 
ture also affects the density of water ; if 1,000 cubic inches 
of water at the freezing-point be heated to the temperature 
of a hot summer day, its volume will be increased seven or 
eight cubic inches. The differences in temperature and 
density have far-reaching results ; for upon these varia- 
tions the general circulation of the waters of the sea in 
part are due. 

The temperature of the sea varies with both latitude and 
depth. In general, the surface waters of equatorial re- 
gions are warmest, and in the broader extents of the sea 
their temperature is not far from 26° (79° F.). Toward the 
poles it gradually falls, and in polar regions it is rarely 
much above the freezing-point. The variation of temper- 
ature with latitude is by no means uniform, however, for 
in various places warm water dragged by the " skin fric- 
tion " of winds is frequently found in high latitudes. 

With relation to depth the variation is remarkably uni- 
form. In low latitudes the bottom temperature of deep 
water is a degree or two above the freezing-point of fresh 
water ; in polar latitudes, a degree or two below it. In 
shallow waters and land-locked basins, however, the varia- 
tions in temperature are usually very irregular. Thus, the 
entrance to the Gulf of Mexico is blocked by a submarine 
ridge whose crest is 1,200 feet below the surface, and be- 
cause of this, water whose temperature is lower than that of 
the 1,200-foot level cannot enter the Gulf. But even at a 
depth of 12,000 feet, the temperature varies but little from 
that of the 1,200-foot level. 

The freezing temperature of salt water is lower by two or 
three degrees than that of fresh water, the difference de- 
pending mainly on the amount of mineral salts in solu- 
tion. The ice of the sea is therefore formed in high lati- 



WAVES, TIDES, AND CURRENTS 



193 



tudes, where the temperature is much below the freezing- 
points 

Sea-ice takes various forms. 3 The nearly level and nar- 
row shelf that in polar regions forms along the shore, and 
skirts almost its entire extent, is called the ice foot Any 
considerable extent of undisturbed or unbroken ice forms 
an ice-sheet or ice-field. When on-shore winds become so 
strong that the ice-field is crushed and piled up against the 



O 




ICE OF THE SEA : FLOE, PACK, AND BERG. 

shore, it forms pack-ice} Detached masses floating about 
constitute floes; finely broken ice floating on the surface 
constitutes sludge. 

A small part of the ice is caught by currents and winds, 
and carried into warmer latitudes, where it finally melts. 
By far the greater part, however, never leaves polar re- 
gions ; possibly in a few instances it accumulates, but 
most of it melts during the brief polar summer. A certain 
amount of ice certainly floats into temperate latitudes, in 



194 



PHYSICAL GEOGRAPHY 



the form of icebergs, but this ice is not born of the sea : it 
is fresh water ice that is formed on land, and, in the form 
of glaciers, moves down the slopes until it breaks off. 5 

Waves. — The alternate rising and falling of successive 
ridges of water form waves. They vary in size from the 




STORM WAVES : SURF BREAKERS. 



tiny-ripples made by a summer breeze, to the huge billows 
that toss the largest ships. 6 Every body of water upon the 
earth is swept by waves, and these are caused by the fric- 
tion of the air against the surface of the water. 7 

The motion of the water of the wave is simpty up and 
down, with a possible rotatory movement ; and if the wind 
ceases for a moment, the theory holds true. Under a 



WAVES, TIDES, AND CURRENTS 195 

strong wind, however, the top of the wave is pushed for- 
ward, and if the gale be very strong it breaks into foam, 
forming " white caps " and " scud." Before the strongest 
storm-winds not a little water is blown into spray, and the 
whole surface of the ocean is covered with foam. 

When waves roll in upon a shallow coast their motion 
is also modified. The moment the bottom of the wave 
touches ground it begins to drag. The top of the wave, 
on the contrary, not being impeded, advances more rapidly, 
and finally combs or falls forward, making breakers. The 
water and foam that flow upon the shore constitute the 
surf. 

The distance from the shore at which waves begin to 
comb depends partly on the depth of the wave, and partly 
on the depth of water along the shore. Ordinary waves 
rarely exceed three or four fathoms in depth, and therefore 
they do not comb until they are within a few rods of shore. 
Along certain shores of the Indian Ocean, on the other 
hand, where the coast waters are shallow and the waves 
are deep, the latter begin to comb at a distance of three 
or four miles from shore. 

For the formation of the highest and largest waves, a 
deep, open sea is required, and in general the largest waves 
are found in the broadest expanse of water. In calm 
weather, the waves of the open sea are from six to ten 
feet in height ; their breadth is about ten times the height. 

With a wind of twenty or thirty miles an hour, the 
height of the wave is somewhat increased; its breadth is 
materially greater, and the largest steamships pitch con- 
siderably as they ride over them. With the wind at sixty 
or eighty miles the breadth of the wave is increased to 
about two thousand feet ; its height may reach twenty or 
thirty feet, and its progressive velocity may reach forty 
miles an hour. 



196 PHYSICAL GEOGRAPHY 

It is a common belief that the waves run highest when 
the wind is at its maximum velocity. This is not the case, 
however ; they do not reach their greatest height until the 
lull of the wind ; 8 then they sometimes roll to a height of 
forty-five or fifty feet. 

The force with which waves strike an opposing surface 
is greater than is generally imagined. . Measurements on 
the coast of Scotland, show that ordinary calm-weather 
waves have a striking force of six hundred pounds per 
square foot ; that of the heaviest storm-waves is about ten 
times as great. 

In navigation it is found that the chief damage from 
storm- waves is due to the battering that the lighter wood- 
work above deck receives. 9 In recent years the old cus- 
tom of spreading oil on the surface to the windward has 
been revived. 10 The oil covering the water presents a 
surface that offers comparatively little friction to the wind. 
As a result the waves, although rolling high, no longer 




THE TIDE WAVE: MOON IN CONJUNCTION 

break upon the vessel. The latter, therefore, is often 
enabled to withstand storm-waves that otherwise would 
demolish everything above her decks. 

Notwithstanding their tremendous energy, waves are 
superficial. The effects of ordinary, calm-weather waves 
do not extend more than a few feet below the surface ; 
the fiercest storm-waves do not reach more than two hun- 
dred feet below the surface. 



WAVES, TIDES, AND CURRENTS 197 

Tides. — The alternate rise and fall of the sea-level 
twice a day is a phenomenon familiar to everyone who 
has visited the seashore. For six hours the level of the 
water, little by little rises, overflowing the shore and fill- 
ing the river estuaries. For a few moments, the water is 
stationary, and then for about six hours it falls — ever 
repeating, never ceasing its oscillations. 

Excepting certain estuaries and bays, neither the high 
nor the low water level varies much throughout the year. 
As the level rises and the water flows in upon the shore, 




THE TIDE WAVE : MOON IN OPPOSITION 

the tide is flood ; as it recedes it is ebb ; its highest level is 
high water, and its lowest low water. During the few 
minutes at the turn of the tide it is slack water. 

This rise and fall of water is ascribed to the attraction 
of the sun and the moon ; in its nature, the movement of 
the water is practically a wave several thousand miles 
broad. Both the sun and the moon attract the earth. 
The solid portion of the earth being rigid, however, does 
not perceptibly bend or yield ; the water envelope, on 
the contrary, is drawn into the elongated form," giving 
the appearance of two wave-crests, one on each side of the 
earth. No matter whether the sun and the moon are 
on the same side, or on opposite sides, their combined 
attraction will produce the same results. If, however, 
they have the position, so that they pull at right angles, 
four tide-waves will bo formed — two of the sun and two 
of the moon. 




THE TIDE: MOON IN QUADRATURE 



198 PHYSICAL GEOGKAPHY 

In most of the Northern Hemisphere, where the great 
land masses interrupt the progress of the tide-waves, the 
solar tides are merged into those of the moon. Only in 
the broad expanse of the ocean, in the islands of the 
South Pacific, are they distinguishable. When their 

effects are added to or 
subtracted from the lu- 
nar waves, however, the 
difference is consider- 
able. Thus, at new and 
full moon, when the pull 
is exerted in a straight 
line the tides are some- 
what higher at flood 
and lower at ebb ; these are the spring tides. When the 
attraction is exerted at right angles they are neap tides. 
In some instances the spring tides are twice as high as 
the neap tides. 

Thus it seems that the moon by its attractive force lifts 
the waters of the sea into two great waves. Moreover, as 
the moon revolves around the earth, these waves are each 
dragged around at the same time, in much the same 
manner as though they were fastened to it, each making a 
passage in about twenty-eight days. 

But while these waves are making each its revolution, 
the earth at the same time is turning on its axis, every 
twenty-four hours. The daily motion of the tides, there- 
fore, results from the earth's turning on its axis. Every 
point on the earth, accordingly, overtakes and passes the 
two waves daily, very much as though it were slipping 
under them. 

If the surface of the earth were covered with a uniform 
depth of water, the direction of the tide-waves would be 
from east to west. As a matter of fact, the position of the 



WAVES, TIDES, AND CURRENTS 



199 



continents prevents any such uniform direction. Every 
mass of land is an obstacle in the path of the advancing 
wave, and inasmuch as the latter cannot sweep over a con- 
tinent, it must pass around it, or be checked. 

Only in the broad, open waters of the Southern Hemi- 
sphere do the tides move in their theoretical direction from 
east to west. In the North Atlantic the wave is turned 




CO-TIDAL LINES 
The lines show the position of the erest of the tide-wave for each two hours. 



to the northward, and, entering the Arctic Ocean, it is 
diverted to the eastward. 12 

The height of the tides is also affected by the land 
masses. In mid-ocean the difference between high water 
and low water is scarcely three feet. Along the coast of 
the United States it varies from four to ten or twelve feet. 
From New York to Savannah spring tides are about five 
feet, and neap tides about four feet. In the Gulf of 
Mexico the rise and fall is only about one-half as great ; 



200 PHYSICAL GEOGEAPHY 

along the Maine coast it is ten or twelve feet; and at 
Sitka, Alaska, from twenty to thirty feet. 

The great difference is dne chiefly to the shape of the 
shores. If the tide-wave faces a V-shaped estuary the 
advancing body becomes constricted by the narrowing 
shores. Not being able to spread out sideways, it is 
therefore increased both in depth and velocity. In Minas 
Basin, at the head of the Bay of Eundy, at times the water 
advances as a solid wall twenty or thirty feet high. The 
piling up of tide-Avaters in the form of a wave is commonly 
called a bore. It is a marked feature in the Amazon, the 
Ganges, and the rivers of the China coast. It is also 
noticeable in many of the estuaries of the British Isles. 
The spring tide in Bristol Channel is sometimes forty feet. 

In many instances the shape of the shore is such that 
the waters of the advancing tide are separated by an 
island lying near the shore, again uniting in the narrow 
strait between the mainland and the island. As a result 
eddies and dangerous whirls are formed. Thus, at Long 
Island the advancing wave is divided, one part entering 
New York Bay, the other, Long Island Sound. The two 
currents meet in the narrow Hell Gate, or "whirling strait." 
The Maelstrom, an eddy formed by the Lofoten Islands, 
off the coast of Norway, is a similar current. 18 

Ocean Currents. — Throughout the greater part of its 
extent the sea is traversed by currents that flow in defi- 
nite directions with a fairly uniform velocity. The water 
of an ocean current has an energy of its own, and its mo- 
tion is practically the same as though it were flowing from 
a higher to a lower level. There are other instances, how- 
ever, in Avhich the movement is almost entirely caused by 
the wind, the direction being wholly a result of the wind. 
The wind-blown waters are called drifts. Currents are 
deep, sometimes extending to the bottom ; drifts, on the 



202 PHYSICAL GEOGRAPHY 

other hand, are superficial. The current may gradually 
become a drift, and a drift may become a current. 

The winds, and the unequal heating of the waters in 
equatorial and polar regions are thought to be the main 
causes of the general movement of ocean waters ; the 
winds and the rotation of the earth on its axis are the 
chief factors that make them currents and determine 
the direction of their flow. 14 The water in equatorial re- 
gions receiving the vertical rays of the sun is heated to 
a higher temperature than the water in higher latitudes. 
Being expanded a flow toward polar regions occurs. At 
the same time cooler water flows toward the equator in the 
form of an undercurrent. Thus a constant circulation is 
taking place — a surface movement from equatorial to po- 
lar and an undercurrent from polar to equatorial latitudes. 
This general movement is modified by the winds — and 
undoubtedly by the rotation of the earth. 13 

In equatorial latitudes the prevailing direction of the 
wind is toward the west, and this gives the waters a west- 
erly movement. A flow of water, nearly 1,000 miles broad, 
called the Equatorial Current, is the result, and, except at 
the places where it is interrupted by the continents, it 
girdles the earth. Its flow is scarcely more than a drift, 
and its rate is about ten or fifteen miles per day. Most 
of the warm currents of high and temperate latitudes are 
branches of it. 

The Atlantic part of this current is divided at the east- 
ern angle of South America. The southern branch flows 
along the eastern coast of this grand division for nearly 
2,000 miles ; what is its name ? Gradually losing its 
energy it becomes a drift, and finally it returns to the 
equatorial current. Describe the course of the northern 
branch ; what is its name after it emerges from the Carib- 
bean Sea? The Pacific part of the Equatorial Current is 



WAVES, TIDES, AND CURRENTS 203 

more than 9,000 miles long. At the edge of the Eastern 
Continent it is again divided; what is the name of the 
northern branch ? of the southern ? Describe the circuit 
of each. In the midstream of the Equatorial Current is 
found a narrow belt of water flowing in the direction op- 
posite that of the main stream. It is called the Equa 
torial Counter Current ; no satisfactory explanation for it 
is known. 

The Gulf Stream is by far the most important of the 
currents of the Atlantic Ocean ; why ? Its sources are in 
the Caribbean Sea. A part of its volume flows through 
Santarem Channel ; a greater part is gathered into Yuca- 
tan Channel ; a small but measurable part is drawn from 
the Gulf of Mexico. These branches unite in Florida 
Strait, and here the stream as a definite current begins. 

At Florida Strait its velocity varies from three and one- 
half to five and one-half miles an hour. 16 To the north- 
ward it gradually decreases until, off the Labrador coast, 
it ceases to have any motion of its own ; thereafter it is a 
drift dragged by westerly winds. 

The Gulf Stream is not only the swiftest of ocean cur- 
rents, but it is also the warmest. Off the Florida coast 
its summer temperature is 30° (86° F.), and even near the 
Greenland coast it is twenty or thirty degrees (F.) warmer 
than the surrounding waters. Contrary to common opinion, 
it is not a shallow current. As a matter of fact, from Flor- 
ida Strait to Cape Hatteras, it extends to the bottom of 
the ocean. Its drift is pushed northward and eastward, 
and much of it forms a circuit returning to the Equatorial 
Current. A considerable volume, keeping northward, finds 
an entrance to the gulfs and bays of western Europe, reach- 
ing even to the north coast of Norway. 

The Kuro Siwo is the Gulf Stream of the Pacific. 
Some of its waters issue from the Bay of Bengal, but the 



204 PHYSICAL GEOGKAPHY 

greater part of its volume passes among the Malaysian 
Islands. Thence it flows along the eastern coast of Asia. 
Off the Japan Islands it becomes a drift, and its waters 
are then pushed by the prevailing winds toward the North 
American coast, performing an oval-shaped circuit like 
that of the Gulf Stream. 

The Kuro Siwo is not only a much feebler current than 
the Gulf Stream, but it is a cooler stream as well. Its 
summer temperature rarely exceeds 22° (72° F.), and its 
winter temperature is not far from 17° (63° F.). In sum- 
mer it extends as far north as the Kuril Islands ; in win- 
ter it scarcely reaches the Japan coast. Recent surveys 
show that, contrary to common opinion, no part of the 
Kuro Siwo enters the Arctic Ocean through Bering Strait. 
In a few instances only has a setting of water into the 
strait been observed, and these have resulted from strong 
southwesterly winds. The prevailing movement in Bering 
Strait is a feeble flow from the Arctic Ocean. 

It has been definitely ascertained that much of the cir- 
culation of the colder waters of the ocean takes the form 
of undercurrents, but no survey of an undercurrent has yet 
been made. Two very definite surface currents of water 
have been observed, however, and their position is fairly 
well known. These are the Arctic Currents. One of them 
flows southwards along the east shore of Greenland, finally 
turning into Baffin Bay ; the other flows on the west shore 
and, emerging into the Atlantic, meets the Gulf Stream off 
Newfoundland. 

Off the coast of Cape Hatteras, almost in the track of 
the Gulf Stream, is an adverse current known on pilot 
charts as " Little Hell." It is marked by heavy, choppy 
waves, and persists, even in the face of a strong southerly 
wind. Its waters are cold, and it is thought to result from 
the rising of an arctic undercurrent to the surface. 



WAVES, TIDES, AND CURRENTS 205 

The Antarctic Current is the chief movement of cold 
water in the southern hemisphere. It is a drift rather 
than a definite durrent, however. Its waters are several 
degrees cooler than those with which they finally com- 
mingle. 

Economy of Ocean Currents. — One of the chief and 
most important effects of marine currents is the equalizing 
of the temperature of ocean waters. Without this inter- 
change the heat of equatorial waters would sooner or later 
become fatal to many forms of life, aud the polar ice-caps 
would intrude far into temperate latitudes. The more 
practical effects are seen by comparing the coast of Labra- 
dor with that of the British Isles, in the same latitude. 
The harbors of the former are blocked with ice for five or 
six months of the year ; the latter is open the year round. 
The former is bathed by cold waters ; the latter by the 
drift of the Gulf Stream. The port of Hammerfest, situ- 
ated within the Arctic circle, is an open harbor free from 
obstructive ice all the year round. It is very doubtful if 
warm currents have any perceptible effect on the tempera- 
ture of a region at any considerable distance from the 
coast, but that they keep the coast free from ice is beyond 
question. How does this affect commerce? 

Evaporation is very great along the courses of warm cur- 
rents and the moisture borne with the wind adds no little 
to the rainfall of the regions. When the moisture is con- 
densed the latent heat set free adds warmth to the region. 
Cold currents have a chilling effect on the air, and if the 
latter has much moisture it is apt to take the form of fog. 
The Newfoundland and Labrador coasts probabl} T get their 
dense fogs in this way. Ocean currents thus are indi- 
rectly factors in climate. 

Sargasso Seas. — Within the ovals formed by the 
branches of the Equatorial Current and their drifts there 



206 PHYSICAL GEOGRAPHY 

are extensive accumulations of marine plants. These were 
named by Spanish navigators Zargazzo, or grassy seas. 
The accumulations have been sometimes attributed to the 
eddying motion of the current and its drift, but of this 
there is little or no evidence. Calm water is necessary for 
the growth of these species forming the accumulations, and 
they occur most frequently in such localities. 

Physiographic Effects of Oceanic Movements. — 
So closely related to one another is the work of waves, 
tides, and currents, that their physiographic effects can- 
not well be separated one from the other. In general the 
work of waves is both destructive and constructive — they 
not only tear away coasts, but they build them as well. 
On the other hand, the work of tides and currents is 
mainly transporting — they carry material from one place 
to another. Although waves act only at the surface, their 
work is none the less effective, and throughout the whole 
extent of coast one or the other of two things is con- 
stantly going on — material is either being removed from 
the shore or else it is being added to it. 

The rugged outlines of coasts to a considerable extent 
are results of wave action. The softer parts are worn and 
broken, while the harder portions that remain largely con- 
tribute to the frayed appearance of the coast. 17 At first 
the harder rock projects in the form of long arms ; then 
these are broken, leaving a multitude of rocky islets. 

Along the coast of the South Atlantic States, the effects 
in places are still more noticeable. The shores of Cape 
May, New Jersey, are wasting away at the rate of several 
feet a year, and those of Charleston Harbor require almost 
constant repair, so destructive is the incessant pounding 
of the waves. 

On the east coast of England, owing both to waves 
and swift tidal currents, the yearly waste is considerable, 



WAVES, TIDES, AND CUREENTS 207 

and since the time of Henry VIII. a belt about one mile 
in width has been shorn from the Kent coast. 18 Along 
the west coast of Scotland, and especially among the 
Hebrides Islands, are many thousand rocky islets rising 
from the sea like spectral watch-towers. They are all that 
remain of a former coast as witnesses of the destructive 
force of the waves. 

As its name indicates, a cliff-girt coast is one that is 
bordered by steep or by vertical cliffs. The chalk cliffs 
of Dover, England ; the cliffs at Newport, Rhode Island ; 
and almost the whole extent of the California coast are 
examples of this type. Generally there is a narrow strip 
of sandy beach between the cliff and the water's edge, but 
sometimes this is absent. In every case the cliffs are 
shaped by the action of Avaves. On account of a slow sub- 
sidence of the coast, the sea has encroached on the land, 
and little by little, the waves have undermined and bat- 
tered down the shores. 

The constructive and building power of waves is finely 
shown along the coast of the South Atlantic and Gulf 
States and that of the Netherlands, the most noticeable 
feature of Avhich is the multitude of spits, barrier beaches, 
and islands that border it. 

In the building of shores not a little depends on the 
position and direction of tides and local currents. If the 
latter strike the shore broadside, or at right angles, the 
bars and spits take the shape so common along the Gulf 
coast. On the other hand, if they impinge upon the 
shore obliquely, the sand and sediment are caught by the 
swirl of the current, and deposited in curved forms vari- 
ously known as saw/// hooks. 

Forms of this character are the rule along the Massa- 
chusetts coast. Cape Cod, Monomoy Point, and Nan- 
tucket Beach are nothing 1 tut sandy hooks ; Marthas Vine- 



208 PHYSICAL GEOGRAPHY 

yard and Nantucket Islands contain half a score of such 
examples. Sandy Hook Peninsula, now an island and an 
obstruction to the navigation of Lower New York Bay, is 
one of the most striking examples. Find similar examples 
on the shores of the North and Baltic Seas. 

The effects of the tide in scouring out estuaries have 
already been noted, but there are certain effects of tidal 
currents that, at first, are not obvious. Waves are capa- 
ble of battering down a cliff, but they are not able to re- 
move the material, and this, in time, lodging at the foot of 
the cliff, would protect it from any further assaults of the 
waves. But if the tidal currents remove this material, the 
waves have an unprotected surface upon which to work. 

The bars at the mouths of rivers are nearly always the 
work of tidal currents, and so are rnairy of the " banks " or 
shoals that obstruct straits and sounds. The North Sea 
contains many examples, and Lower New York Bay is so 
full of them that only a small part is available for deep- 
draught vessels. 

Ocean currents undoubtedly transport an enormous 
amount of material. The Gulf Stream sweeps the shells of 
certain marine organisms from the Caribbean Sea as far 
north as the Carolina coast. The icebergs floated by 
arctic currents bring down a large amount of gravel and 
bowlders which are finally dropped in lower latitudes. 
Both the bank on which the Florida Beefs are built, and 
that on which the Bahamas have been formed, are thought 
to have been the work of marine currents. It is by no 
means impossible that constant deposition of matter car- 
ried by ocean currents may have resulted in extensive 
changes of level in various parts of the earth's surface. 



QUESTIONS AND EXERCISES.— If possible, evaporate a small 
quantity of stream water of any kind in a beaker, or a porcelain dish, 



WAVES, TIDES, AND CURRENTS 209 

and note the result. Repeat the experiment with rain water. What 
inferences can be drawn that are applicable to the second paragraph of 
this chapter? 

Prove that ice, bulk for bulk, is lighter than water. 

If possible observe the effects of waves on the shore of any conven- 
ient body of water. Note the character of the work they do, or that 
you find they have done. Explain how waves make beach sand. 

If you are near the ocean, find the season of the year when the tides 
are highest. 

Refer to the map, p. 199, and note the direction of the tide waves in 
various parts of the Atlantic Ocean. What is their general direction in 
the South Pacific ? 

Explain how ocean currents may affect navigation, either favorably 
or adversely. 

In one of the first chapters of his narrative, Robinson Crusoe speaka 
of the great indraught of the Gulf of Mexico ; what feature is meant ? 

Of several thousand sealed and registered bottles thrown into the 
Gulf Stream, off the Florida Coast, a number were found afterward in 
the Caribbean Sea, along the West Indies ; from the current chart, p. 
201, explain their movement. 

From any available cyclopedia, or other work of reference, prepare 
an account of one or more of the following : the Gulf Stream, the Mael- 
strom, the bore of the Amazon, the tides of the Bay of Fundy, the 
Hell Gate, or the effects of storm-waves. 

COLLATERAL READING AND REFERENCF. 

Pillsbury. — The Gulf Stream. United States Coast Survey. 

Mill. — Realm of Nature, pp. 154-184. 

Shaler.— Sea and Land, pp. 1-74, 187-222. 

U. S. Hydrographic Office.— Use of Oil in Storms. 



NOTES. 

1 Color names are of frequent occurrence in the nomenclature 
of the arms of the sea. The color of sea-water is both apparent 
and real. The apparent hue is often due to reflection from the 
sky ; the real color to the substances in solution. Shallow water 
is commonly greenish ; deep water a dark blue. The water of 
the Gulf Stream has a peculiar blue color and is instantly dis- 
tinguished from the lighter colored water on either side. The 



210 PHYSICAL GEOGKAPHY 

phosphorescence of sea- water, usually observed in warm regions, 
is due to a microscopic organism, Noctiluca miliaria, that, like 
the common firefly, has the power of emitting light. At times 
the wake of a vessel seems like a track of fire. 

2 Bulk for bulk, ice is lighter than water. Solid sea-ice floats 
with about one-eighth of its mass above the surface. If it con- 
tains air-bubbles, however, a greater proportion is out of water. 

3 In a few instances the formation known as anchor ice takes 
place. It results from the freezing of fresh water at the bottom 
of an estuary into which salt water flows. The ice accumulates 
on the bottom until its buoyancy overcomes the force with which 
it adheres to the bottom ; then the whole mass rises to the surface. 
It receives its name from the fact that it is very apt to begin 
forming about anchors or other metallic substances lying at 
the bottom. In certain cases these have been lifted from the 
bottom and floated. In some instances large areas of anchor-ice 
have become suddenly detached from the bottom, and the estu- 
ary, a few minutes previously free from ice, becomes filled with 
sludge. This form of ice is also called ground-ice. 

4 The formation of the pack is sometimes sudden and frequently 
violent. The crunching from side-pressure is so great that not 
only is the ice piled up in huge blocks, but the blocks, often 
weighing many tons, are shot up into the air ten or twenty feet. 

6 The difference in the form of the Greenland and the south 
polar icebergs is due to the character of the glaciers from which 
they are broken. Antarctic glaciers are derived from sheets of 
land ice ; Greenland bergs, on the contrary, are derived mainly 
from the hummocky ice of glaciers that flow in ravines. It is 
commonly asserted that most of the icebergs floating down 
through Davis Strait come from Humboldt Glacier. As a matter 
of fact scarcely a single one comes from this quarter ; they nearly 
all come from Disko Bay. 

6 A breeze of two miles an hour throws the surface of still 
water into ripples two or three inches broad and not far from an 
inch in height. The slope of the wave is rarely the same on both 
sides. The wind pushes the crest forward so that the front of the 
wave is considerably steeper than the back. Large waves as a 
rule result from the union of smaller ones, and this process goes 
on until, finally, the accumulation is the greatest mass that the 
breeze of the given velocity can move. 



WAVES, TIDES, AND CURRENTS 211 

1 Strictly speaking, it is a matter of adhesion rather than fric- 
tion, and when the wind blows over the surface of still water the 
lower surface of the air actually remains in contact with the 
water. In a stiff gale the dragging force exerted on the surface 
of the water by the wind amounts to a little more than one 
ounce on each square yard of surface. 

8 The effect of the wind is to push their crests forward rapidly, 
practically flattening them. 

9 A stanch vessel with her head to the wind need fear but little 
from the waves. The latter may smash everything above deck, 
but the hull will ride the waves safely so long as they do not 
board her. Riding so that the waves strike broadside, however, 
is a different matter, and no vessel can accomplish it without 
danger of foundering. The danger from waves arises not so much 
from their height but from the possibility of their breaking upon 
and boarding the vessel. Otherwise a ship can ride waves of sixty 
feet as safely as those of six. 

10 In the use of oil and similar substances two results must be 
studied — namely, to prevent the growth of waves, and to prevent 
their breaking. In the great majority of instances, however, the 
problem befoi-e the sailing master is to prevent the breaking of 
waves. For this purpose it is found that sperm oil and oil of 
turpentine are the best. In use, the oil is poured into a coarse 
canvas sack and the latter is floated to the windward of the ves- 
sel, being held in position by any convenient outrigging. The 
oil oozing through the canvass spreads rapidly over the surface of 
the water. Instantly the waves, though they may run high, cease 
to break. The following from the log of the Swedish brigantine 
Drott is one of a great many similar testimonials gathered dur- 
ing the past few years by the United States Hydrographic Office : 
" I had seen upon the pilot chart that oil had been used with 
good effect in calming heavy seas. I started to try it and had two 
bags made of the capacity of two gallons each. These bags were 
stuffed full of oakum, and then one gallon was poured into each, 
half fish oil and half petroleum. A very small hole was cut in 
the bottom of each bag which allowed the oil to drop out freely. 
One of these bags was suspended from each cathead, just out of 
the water, and the result was simply a wonder to me, so much 
so that I could hardly believe my senses. No more seas were 
shipped and all hands turned to secure the main hatchway prop- 



212 PHYSICAL GEOGRAPHY 

erly, which was impossible to do before on account of the risk of 
being washed overboard. The former combers were now great 
rollers only, not a sea breaking nearer than thirty feet from the 
vessel. The crew were now able to pump out the ship and clear 
up the decks in perfect safety. About 11 p.m. the sea broke over 
the starboard side and smashed in one of the boats, but this was 
found to be due to the loss of one of the oil bags, and as soon as 
another was put out and kept supplied with oil no more waves 
came on board." 

11 This theory of the tides is not accepted by all astronomers. 
See Appendix, Table VI. 

12 At Lady Franklin Bay, Lieutenant ( now General ) Greely 
observed that the tide came from the north. 

13 During pleasant weather the eddy of the Maelstrom is hard- 
ly noticeable during slack water, or at the time of neap tides. 
When the flood or the ebb of spring tides is strong, however, the 
current is strong, and, with a hard northwest wind, it is a dan- 
gerous locality. 

14 According to Herschel and Carpenter the winds themselves 
pile up the waters in equatorial latitudes, thereby bringing about 
a condition of inequilibrium. Lieutenant Maury held that the 
difference in specific gravity between the saltier waters of equa- 
torial and the fresher waters of polar regions is competent to 
account for ocean currents. That each is an important factor 
cannot be denied. 

15 Owing to the turning of the earth on its axis, a point on the 
equator travels 25,000 miles in twenty -four hours — a speed of 
about 1,000 miles an hour. In latitude 60° it is only half as 
much. Consequently water flowing from latitude 60° toward the 
equator, every point of which has a greater velocity, has a ten- 
dency to lag behind. 

16 The velocity varies not only with the season, but also with 
the age and the passage of the moon — that is, the variations are 
yearly, monthly, and daily. The velocity is greatest during sum- 
mer and least in winter. The position of the axis of the stream, 
or line of swiftest flow, changes also with the season. An adverse 
wind will retard ; a favorable wind will increase its velocity. 
A quartering wind or one blowing athwart is apt to push some of 
the surface water out of the track of the stream, at the same time 
pushing colder water into it. The fact that Gulf Stream water 



WAVES, TIDES, AND CURRENTS 213 

is occasionally pushed against the coast has more than once 
given rise to the statement that its position is subject to change. 

17 Glaciers and glacial action have also had much to do with 
the shaping of surface features of these coasts . The coasts of Ire- 
land, Norway, Alaska, and Chile much resemble that of Maine. 
Their general outline, however, is due to submergence ; with the 
lowering of the level of the land, the waters cover the valleys. 

'" During the reign of Henry VIII. the church of Reculver stood 
at the distance of a mile from the shore, but the sea now laves 
its foundation stones. The famous Goodwin Sands, a shoal about 
twenty square miles in extent, southeast of Kent, was formerly a 
part of the mainland. In the twelfth century, during a severe 
storm, this area was washed away by the sea, and has been cov- 
ered with water ever since. The channels through this shoal 
shift with every storm. 



CHAPTER XII. 
THE ATMOSPHERE AND ITS PROPERTIES : WINDS 

The atmosphere, or air, is the gaseous substance that 
forms the outer envelope of the earth. It rests on the 
land and the water, and probably penetrates both to a 
considerable distance. Being a part of the earth, the 
atmosphere partakes of all the general motions of the lat- 
ter, but it has also certain movements of its own, and 
these are very closely connected with life and its envi- 
ronment. 

The air is not a simple, or elementary, substance ; as 
noted on p. 22, it is a mixture of several elements. The 
chief constituents, nitrogen and oxygen, have the propor- 
tion of about four parts of the former to one of the latter, 
and the proportion does not change materially. The re- 
maining constituents, water vapor, carbon dioxide, and float- 
ing matter vary greatly. The vapor of water rarely exceeds 
one part in one hundred of air. It is nevertheless a most 
important constituent, for it is in this form that the water 
is borne from the sea and shed upon the land. The floating 
particles of smoke, dust, and other matter are also essen- 
tial, for they aid materially in condensing the water vapor. 

The air is highly elastic. Stop the nipple of a bic} r cle 
pump and push the piston quickly; note what occurs. 
Pressure, therefore, decreases the volume, making the air 
denser. When the pressure is relieved, the air again 
expands and is less dense or rarefied. 1 Air next the 
ground is denser than that above, because of the pressure 

314 



THE ATMOSPHERE AND ITS PROPERTIES 215 



or weight of that overlaying it. The density decreases 
with the distance above the sea; at an altitude of two 
miles the density is only two-thirds that at sea-level. At 
sea-level a cubic foot of air weighs a little more than one 
Troy ounce. 

The force with which the air presses upon a given sur- 
face is called its tension ; and, practically, the tension is 
a form of expressing its pressure ' on the 
rock envelope. At sea-level, the column 
of air rests upon the surface with a press- 
ure of about fifteen pounds on every square 
inch, or a little more than a ton on each 
square foot of surface. The tension varies 
slightly in different latitudes, being a little 
greater near the tropics than elsewhere. 

It is most convenient to estimate the 
tension of the air by observing the height 
of a column of mercury, or quicksilver, that 
will just balance it. The instrument used 
for this purpose is called a barometer. It 
consists of a glass tube closed at one end, 
and filled with mercury ; the open end is 
placed in a small cup filled with mercury. 
The pressure of the air on the surface of 
the mercury in the cup keeps the column 
in the tube in place. If the column in the 
tube rises it signifies that the pressure of 
air overhead is increasing ; if it falls, the 
pressure is decreasing. The weight of the 
mercury in the tube is just equal to that 
of a column of air, having an equal base, and the two 
balance each other. 

The atmosphere is warmed partly by the direct rays of 
the sun and partly by the heat radiated from the earth. 



y 



THE BAROMETER. 



216 PHYSICAL GEOGKAPHY 

It is also heated by compression and cooled by expan- 
sion. When a volume of air is compressed, it becomes 
greatly heated. Thus, air that descends from higher to 
lower levels, becomes heated because it moves into a. re- 
gion where the density and tension are greater. In the 
same way, a volume of rising air expands and is cooled, 
because it goes into a region where the tension and density 
are less. Heat causes the air to expand and, bulk for bulk, 
warm air is therefore lighter than cold air. 3 If a volume 
of air is warmed from freezing -temperature to that of in- 
tense summer heat its volume is increased nearly one-fifth. 

The temperature of the air varies both with latitude 
and with altitude. In equatorial latitudes the mean tem- 
perature of the air over the sea is not far from 32° 
(90° F.) ; in polar regions it ranges much below 0° (32° F.). 
With respect to altitude there is a fall of temperature at 
the rate of about one degree for every three hundred feet 
of ascent. The effect is very noticeable in the equatorial 
Andes. At the base of the mountains the heat is intense ; 
at an altitude of ten thousand feet the air is mild and 
pleasant ; at seventeen thousand feet one lives in a region 
of perpetual snow. 

Movements of the Atmosphere. — Like the waters 
of the sea, the air is everywhere in motion. The move- 
ments are both general and local. The attraction of the 
sun and the moon undoubtedly causes atmospheric tides 
something like the tides of the sea. Their effects, how- 
ever, are very slight, and practically nothing is known 
about them. 

Sensible movements of the air are called winds, and 
they are caused by changes of temperature. When the 
air at some locality or other is heated to a temperature 
higher than that surrounding, it expands and, becoming 
lighter, bulk for bulk, it is pushed upward by the heavier 



THE ATMOSPHERE AND ITS PROPERTIES 217 



air that flows in. In this way winds originate. Such 
movements of the air are everywhere taking place, and it 
is evident that they are examples of the force of gravity. 

Equatorial and polar regions are not equally heated. 
The former receives the almost vertical rays of the sun ; 
the latter onty oblique rays. The air in low latitudes, 
therefore, is warmed and pushed upwards by the inflow of 
colder air. This process results in two great movements, 
namely — a sur- 
face flow toward 
the equator, and 
upper currents 
from the equato- 
rial toward po- 
lar regions. 

But the colder 
air comes from 
the regions where 
the speed of the 
earth's rotation 
is comparatively 
slow, and enters 
latitudes where 
it is much great- 
er ; and not be- 
ing able to acquire this speed at once it lags behind, pro- 
ducing a current to the westward. The rising current 
moves into a region in which the speed of rotation is not 
so great, and therefore moves eastward, as well as toward 
the north. 

Winds are usually named according to the direction 
from which they come. But in the two great movements 
described the easterly and the westerly components are 
much more noticeable than the polar and equatorial inove- 




GENERAL MOVEMENTS OF THE ATMOSPHERE. 



218 



PHYSICAL GEOGRAPHY 



inents. For this reason it is customary to recognize throe 
great belts of winds — a belt of equatorial or easterly, be- 
tween two zones of extra-tropical or westerly winds. These 
general movements are very strongly marked in the oceans, 
but they are greatly modified by the continents ; in inland 
mountainous regions they might escape notice except 
through long-continued observations ; in the great lowland 
plains they are more regular. 

Trade Winds. — The surface winds that flow into trop- 
ical regions to take the place of the warm air that is 







January. 




PREVAILING WINDS OH THK ATLANTIC 



pushed upward, form the well-known Trade Winds. What 
is their direction in the northern half of the belt? in the 
southern half ? Toward the centre of the belt they are 
practically strong, steady easterly winds. 

The zone of Trade Winds is about fifty degrees in width. 
Its position is not stationary ; it swings back and forth, 
north and south, as the seasons change. In the Atlantic 
Ocean the shifting of the belt is not far from eight or ten 



THE ATMOSPHERE AND ITS PROPEKTIES 219 

degrees ; in the Pacific it is slightly greater. The belt 
reaches its northern limit in early autumn ; its southern 
limit in early spring. The winds are regular and constant 
the year round, and their velocity is not far from twelve or 
fifteen miles an hour. 

Formerly, when most of the ocean commerce depended 
on sailing vessels, these winds were of great importance — 
hence their name. A vessel entering the Trade Wind 
belt could rely on steady winds with but little interruption 
from cyclones. 

Along the line where the northerly and the southerly 
components of the Trade Winds meet, there is a narrow 
belt which is characterized by an absence of steady Avinds. 
This belt is the updraught of heated air and is called the 
Equatorial Calms, or Doldrums. This calm belt is scarcely 
more than two or three hundred miles in breadth. Some- 
times vessels were becalmed several weeks in crossing it. 
The wind comes only in fits and puffs, or with an occa- 
sional thunderstorm of great violence. 

Prevailing Westerlies. — The air that flows from equa- 
torial regions as an upper current, 1 in temperate latitudes 
sinks to the surface and becomes a belt of westerly winds, 
now generally called the Prevailing Westerlies ; 5 what is 
their direction in the Northern Hemisphere ? in the 
Southern Hemisphere ? Like the Trade Winds both belts 
move northward and southward with the changes of the 
seasons. 

In the Northern Hemisphere the Prevailing Westerlies 
are neither so strong nor so steady as the Trade Winds, 
and in higher latitudes they often give way to winds of 
northerly origin. On the coast of the Gulf of Mexico the 
Prevailing Westerlies, in the summer season, are reinforced 
by Trade Winds wl licit are deflected by the highlands of 
Mexico. The resulting winds sweep up the- Mississippi 



220 PHYSICAL QEOGEAPHY 

Valley .and thence turn across the Atlantic, carrying with 
them a great deal of the moisture that supplies the East- 
ern United States with rain. 

In the Southern Hemisphere, the Prevailing Westerlies 
are best known as the Roaring Forties. They cover a 
very broad stretch of sea, and they furnish an excellent 
illustration of the theoretical movement of the constant 
winds. When the trade route between Europe and the 
East Indies lay around the Cape of Good Hope, the Roar- 
ing Forties were a very important factor, as the sailing 
master could depend on a twenty or thirty knot breeze the 
year round. It was then a common practice for vessels 
bound for Australia or New Zealand to continue the route 
eastward and return by way of Cape Horn. Trace this 
route on a globe. 

The descent of the upper currents to the surface, which 
is the origin of the Prevailing Westerlies, is marked by 
calm belts — the Calms of Cancer, and the Calms of Capri- 
corn. Like the zones of constant winds the calm belts 
also shift north and south with the season. They are in- 
terrupted by the continents and are scarcely to be noticed 
within a hundred miles of their shores. The Calms of 
Cancer are the well-known " Horse Latitudes." fi The Calms 
of Capricorn are the wider and more continuous of the two 
calm belts. 

Monsoons. — Along many coasts having a southerly or 
a southwesterly exposure the summer winds have a direc- 
tion nearly opposite those of the Avinter season ; that is, 
about half the year they blow/rom the sea; the remaining 
half toward the sea. These winds are called monsoons.' 1 
Two causes operate to give these winds their peculiar 
character — in some instances singly ; in others together. 

In the first place, any great body of land is apt to be- 
come much warmer than the sea in summer and colder in 




iAJVV\ 



222 PHYSICAL GEOGRAPHY 

winter. As a result, during summer there is an updrauglit 
of warm air pushed upward by the inflow of sea air. In 
winter the conditions are reversed ; cold air flows from the 
land to the sea. In other instances, a region may be so 
situated that it is in the southeast Trade Winds at one 
part of the year, and in the northeast part the remainder. 
The monsoons of the Mexican coast are probably due 
to this cause. 

The most remarkable monsoons, however, are those of 
the Indian coast. 8 From April to October the southerly 
half of the belt of Trade Wiuds reaches far inland, pouring 
a deluge of rain upon the land. During the rest of the 
year, on the contrary, the southerly part of the belt has 
reached southward, and the northerly half extends consid- 
erably beyond the coast, parching the land and withering 
vegetation. The tremendous updrauglit of warm air aids 
materially in giving strength to these winds. The " break- 
ing " or change of the monsoon is usually attended by a 
number of terrific storms. 

Along the Gulf coast of the United States the deflected 
Trade Winds of the summer season, noted on p. 218, that 
flow up the Mississippi Valley are replaced by Prevailing 
Westerlies that are turned down the valley. These winds 
may be regarded as monsoons, but they are neither so 
regular nor so strong as the Indian monsoons. 

Day and Night Breezes. — The difference between the 
temperature of day and night is sufficiently great to result 
in stron»gly marked local winds. Thus, along the coasts, 
especially warm regions, the updrauglit of the land causes 
a stiff on-shore wind during the day, while at night the 
air over the land, being more quickly chilled, flows down 
the slopes toward the sea. 9 Thus there results a sort of 
daily monsoon, or day and night local wind. Coast fisher- 
men frequently take advantage of such winds; they go 



THE ATMOSPHERE AND ITS PROPERTIES 223 

out in the morning with an off-shore, and return at night 
with an on-shore breeze. 

Similarly, in mountainous countries the air upon the 
higher slopes is commonly heated and cooled more rapidly 
than in the valleys. As a result there is often a strong 
wind blowing up the valley by day, and flowing downward 
at night. Mountain valley winds of this character are very 
common in almost every rugged country. Which is the 
better indication of the general direction of the wind — that 
noted at the ground, or the movement of the clouds ? 

Local and Variable Winds. — There are many winds 
occurring at irregular intervals that are confined each to a 
particular locality. In most instances these winds are 
confined to desert regions and arid lands, or else they re- 
sult from the proximity of the latter. Almost always they 
are very " dry " winds. 

Thus, the Northers of Texas and Mexico are cold winter 
winds of several days' duration that blow from the high- 
lands of the Plateau region. The Chinook and Santa Ana 
winds of the western highlands of the United States are 
descending, and therefore warm winds blowing from arid 
regions upon fertile lands. In southern Europe they are 
called Foehn winds. 10 The Pamperos are similar winds 
flowing from the cold slopes of the Andes over the arid 
pampas of Argentina. The Punas of the Peruvian table- 
lands are of the same nature. 

In the vicinity of the African desert are the famous 
Mistral and the Etesian winds, both blowing from the 
snow-clad Alpine ranges toward the desert, while the 
Sirocco, like the Chinook, is a hot wind that in summer 
blows from the desert. The Harmattan is a warm winter 
wind, blowing from the desert to the Guinea coast. Aside 
from these there are several winds peculiar to desert re- 
gions. Chief among them is the Simoon, a fierce blast of 



224 PHYSICAL GEOGRAPHY 

liot air and rock waste, that neither man nor beast can face. 
It is common both in the Old World and the American 
deserts. A milder form of this wind along the lower Nile 
valley is called the Khamsin. Classify these winds as 
either hot blasts from the desert, or colds winds blowing 
into it. 

The most interesting of all desert winds, however, 
are the sand whirls. These occur in the morning when 
the air is still — never when wind is blowing. Under a hot 
sun the air next the earth becomes considerably heated, 
having a high temperature. Above the ground the air is 
cooler at the rate of one degree F. for every three hundred 
feet. Thus there is formed the very unstable condition 
of a layer of heavy, cold air on a surface stratum that is 
much lighter. Such a condition cannot last long, and 
sooner or later some slight disturbance or other starts a 
slender column of air upward. 

Immediately the stratum of cold air begins to settle, 
and, as it descends, it forces the warm air upward through 
the self-made passage. The ascending column begins to 
whirl, and soon its motion is rapid enough to carry with it 
a cloud of dust and fine rock waste. 

As a rule these whirls begin when the sun is two or 
three hours high, and continue until the wind begins to 
blow. The latter, by mixing the warm air with the cold, 
prevents their formation until a calm again begins. Oc- 
casionally such whirls develop into very vigorous " sand 
spouts." 

Physiographic Effects of Winds. — As an agent in 
wearing away the surface of the land, the wind acts in dif- 
ferent ways. It may alter the chemical composition of the 
rock with which it comes in contact. It may carry minute 
particles that cut away softer material. It may transport 
material from one place to another. The chemical action 



THE ATMOSPHERE AND ITS PROPERTIES 22.5 



of air is due mainly to the water and carbon dioxide which 
it contains. It is manifested in the gradual crumbling of 
many rocks, when the latter are exposed to the air. The 
rocks most affected are certain iron ores and granite rocks. 
Dry air may affect rocks by chemically withdrawing the 
moisture they contain ; moist air may affect other kinds by 
chemically imparting water to them. In either case the 
rock sooner or later crumbles. 

The impact of minute particles carried by the wind is 
especially noticeable in the western highlands. In regions 




SAND-BEATEN ROCKS 

where sand winds are prevalent the surfaces of the hardest 
rocks are worn, channelled, and polished from this cause. 
Many of the " needles " or rock spires of this region have 
been sculptured into fantastic forms by ceolian or wind- 
blown rock waste. In certain parts of the Colorado and 
Mojave Deserts, telegraph-poles have been cut through in 
a few months by the same agency. 11 

The transporting power of the wind is confined chiHh 
to sea-shores and regions unprotected by vegetation. 
Why? The wave-formed islands and barrier-beaches of 



226 



PHYSICAL GEOGRAPHY 



the Atlantic and Gulf coast have foundations of sea sedi- 
ments, but the above-water part consists of wind-blown 
material. The sand-dunes of sea and lake shores are ex- 
cellent illustrations, and in regions swept by monsoons the 
dunes travel seaward during one season and landward the 
other. A wave of sand about a mile long and seventy feet 
high at one time inundated a part of Cape Henlopen, mov- 
ing at a rate of about fifty feet a year. 12 

Between the silt brought down by the Colorado River, 
and the fierce winds of that region, the Gulf of California 




DUNES OF SAND. 



has been cut in twain, and most of the severed portion 
filled with rock waste to a height now considerably above 
sea-level ; indeed, all through this region dunes are con- 
stantly forming, shifting, and re-forming. In western 
Nebraska, where the rainfall is not sufficient to grow pro- 
tective vegetation, dunes are common. 

Very notable examples of the transporting power of 
wind occur in China. In the basin of the Hoang River 
there are seolian deposits covering many thousand square 
miles to a depth of several hundred feet. These deposits, 



THE ATMOSPHERE AND ITS PROPERTIES 22? 

called loess — from a German word meaning " loose " — are 
thought to come from the desert region to the westward. 
In many places the rivers have cut their channels through 
the loess, and the latter not only colors the water of the 
river, but imparts a yellow tint to the sea into which it 
flows. 

iEolian deposits have filled most of the valleys of the 
Basin Region of the western highlands. The ranges stand 
out in bold relief from an ocean of level rock waste. Many 
of the valleys of the Rocky Mountains have been filled and 
levelled in the same manner. 



QUESTIONS AND EXERCISES.— Devise or describe an experi- 
ment to show that air has weight ; show that it is elastic ; show 
that heating a volume of air causes it to expand ; using a bicycle 
pump, show that compressing air warms it. 

What is the prevailing direction of the wind in the locality in which 
you live? Consult the records of the nearest weather station and com- 
pare- the number of days of westerly winds with the number in which 
the wind is from other directions. 

The tropical calm belts are regions of descending air-currents ; is the 
air apt to be chilled or warmed by this movement ? 

Read Stedman's poem, " The Simoon," and compare it with the 
description in any standard cyclopedia. 

Why are northerly winds apt to be cold ? 

Explain the manner in which street whirlwinds are formed. 

Note any instance of the physiographic effects of winds in the lo- 
cality with which you are best acquainted ; prepare a description of it. 

In what way do the general winds affect the temperature of the 
earth ? 

Note any examples in which winds accomplish work that has an 
economic value. 



COLLATERAL READING AND REFERENCE. 

U. S. Coast SURVEY. — Atlantic Coast Pilot Chart, for March 
and September, or February and August — any year. 
Lb Contb. — Elements of Geology, pp. 1-8. 



228 PHYSICAL (!M()(JltAIMIV 



NOTES 

'At. :i height of fifteen thousand feet the air is so rare that 
breathing is Labored and the pulsations of the heart are very 
rapid. Climbing becomes difficult and any form of exertion is 
very wearying. Water boils al about H. r >" (185° F.), a temperature 
so low that it is difficult l<> cook vegetables l>y boiling. 

J Approximately the pressure Is one-half a pound for every 
Inch in the height of the column of mercury. Al. the level of the 
sea, the height of the barometer varies usually between 29 and 
80.4 Inches. 

:| It is well to bear in mind that the common expression, "hot 
air rises, because it is lighter," is not strictly con-eel. The hoi 
air does not rise ; It is pushed upwards and Honied on the surface 
of the heavier air. 

'The height to which the updniu^lit rises before it turns 
toward the pole is nod known, except, in two or three inslances. 

On the Island of Hawaii, the Trade Winds reach .in altitude 
of about twelve thousand feet. Above this elevation the winds 
have almost an opposite direction; they are the winds that) a 
lew degrees farther north, descend to become the Prevailing 
Westerlies. 

"The Prevailing Westerlies are also called return-trades, anti- 
trades, and counter-trades. The name here used is now com- 
monly employed In meteorology. 

" Many years ago, when most, of the foreign carriage was 
effected by sailing vessels, there was a brisk trade In horses 
between the ports of the New England States and the West 
Indies, nearly all the horses used in the latter country being 
obtained from New England. Frequently the vessels were be- 
calmed in this belt, and it. became necessary to throw overboard 
half the number of horses, in order !<> save the remaining 

animals. 

'The name Is derived from a Malay word, meaning ''season." 

' On account Of its inland position, Central Asia, is marked by 

great extremes of temperature. During summer its vast deserts 

are almost like a, furnace, and the updraught of heated air is so 
enormous that, It causes atmospheric disturbances two thousand 
miles away. In winter the dry air is chilled many degrees below 



THE ATMOSPHERE AND ITS PROPERTIES BB9 

that of the warm Bea-air, and, being correspondingly heavier, 
Mows outward toward the ocean. No other body of land pos- 
sesses the qualities requisite to produce monsoons thai compare 
with i hose of Asia. 

A similar movement of air is noticeable In many large caves 

especially those that have openings at different levels. In the 
daytime air in the cave is usually colder than that outside, 
while .it aighl it is warmer. As a result, at night there is a 
strong in-draught of colder air at the lower entrance, and an up- 
draughl at the higher opening. In the daytime these move- 
ments are reversed. 

'"These three names are applied l<> winds that have certain 

principles in eoiiunon. Warm, moist air is pushed up the side of 

;i mountain-range; being cooled either by its own expansion, <>r 

by contact with the colder intain top, its moisture is con- 
densed ; the air then descending on the other (or possibly the 

s.ime) side warms very rapidly by ils own compression, The 
effect is very marked ; snow disappears very rapidly hence the 
popular mime " snow-eaters." The descending air is noi only 
warm, hut it is so dry thai in summer it withers vegetation. 
The Chinook wind gets its na from a locality in Oregon, 

whence it seemed to come, hut the name is now applied to warm 

winds thai How from the Rocky Mountains out on the plains to 
the Bast. Following a blizzard, if quickly melts the snow that 

covers the scant) teed of the cat t le herds. The Santa Ana is a 

hot dust-driving wind common in southern California and 

Mexico. 

" Some years ago the author left an octagonal steel drill in an 
liprighl posit ion exposed t o t he In 1 1 sweep of a desert wind. Six 
months afterward, when the drill was removed, the angles had 

been almost obliterated by the impact- of rock waste. 

" It is likely that a lire, which in 1828 burned off the vegeta- 
tion protecting the ridge, was responsible for starting this dune on 

its travels. In 1846, General Joseph E. Johnston, (hen a govern- 
ment engineer, noticed thai north Winds were vers actively at 
work in picking Up Sand from tin' seaward face of the dune ami 

carrying it over the crest to the landward side. Little by little 

the wave of saml overwhelmed a strip of pine barrens and Idled 
a Halt marsh beyond. Then it advanced upon a heavy growth of 
timber and, in time, covered all I ml t he tal lest trees, killing them 



230 PHYSICAL GEOGRAPHY 

as effectually as though they had been swept by fire. As the 
years passed by the wave steadily advanced, and the wind began 
to uncover the buried surface in the rear. First the strip of 
pine barrens re-appeared, and then the salt marsh was cleaned 
out and promptly reclaimed by the tide. Even the pine barrens 
began to show signs of life and a growth of young trees sprang 
up. Within the past few years the advancing sand has begun 
to uncover the forest, and a border of dead trees now flanks the 
rear slope. Near the eastern end of the dune is Cape Henlopen 
light-house. A straggling ridge of the wave entered the yard, 
covered up the oil-house and the garden, and then took posses- 
sion of the keeper's cottage. The Government acknowledged 
its inability to cope with the dune by erecting a new cottage on 
the other side of the tower. 



CHAPTER XIII. 

THE MOISTURE OF THE ATMOSPHERE ; SEASONAL 
AND PERIODICAL DISTRIBUTION OF RAINFALL 



The vapor of water mingled with the atmosphere, in a 
way, may be considered a part of it ; 1 but, if all the other 
constituents were absent, the water vapor would exist as an 
atmosphere in itself, and its movements would be the same 
practically as those of the winds. 
But while the proportion of oxygen 
and nitrogen of the atmosphere do 
not perceptibly vary, that of water 
vapor is subject to rapid changes. 
The amount present depends on one 
thing only — temperature. With a 
high temperature there may be a 
great deal of vapor mingled with the 
air ; with a low temperature there 
can be but little. 

Changes in humidity are usually 
apparent to the sense of feeling, and 
one readily learns the difference be- 
tween moist and dry air. 2 In many 
instances they may be forecast by 
observing the clouds. If the latter 
form rapidly, or if small patches of 
cloud increase in size, the humidity 
is increasing. On the contrary, if 
the cloud area is becoming smaller, it is highly probable 
that the humidity is decreasing. 

231 




THE HYGROMETKR. 



232 PHYSICAL GEOGRAPHY 

The amount of moisture is determined in various ways 
Most commonly the hygrometer, an instrument employed to 

measure the amount of moisture, consists of two thermom- 
eters, the bulb of one being covered with a single thickness 
of wet cloth. If the air be dry, the water that saturates 
the cloth evaporates rapidly and chills the bulb, so that 
the reading of the thermometer is several degrees lower. 
If the air is moist, on the other hand, very little evaporates, 
and the difference in the reading of the thermometers is 
very slight. From the difference in the readings of the two 
thermometers the amount of moisture may be calculated. 

Dew Point. — Table VII., Appendix, shows the amount 
of water vapor there may bo in the air at various tempera- 
tures. 3 With the thermometer at 66° F., for instance, 
there may be seven grains in each cubic foot of atmos- 
phere. There might be less, but there can be no more ; 
if more be added it would immediately condense, — that is, 
change to rain or snow. From this table find whether or 
not there may be vapor in the air when the temperature is 
below freezing-point of water. Compare the amount at 
70° F. and 90° F. Learn the temperature at the time of 
recitation, and find the amount of moisture there may be. 
What is the general law shown in this table, so far as tem- 
perature and the percentage of moisture are concerned ? 

When all the vapor that can exist at a particular tem- 
perature is present, the air is said to be saturated or at the 
dew-point. This condition is unusual, however, except 
when rain is falling ; generally the amount present is con- 
siderably less than that required for saturation. From the 
amount present one may easily compute the relative hu- 
midity ; thus, if half the quantity required to saturate the 
air is present, the relative humidity is fifty per cent. What 
is meant when the relative humidity is eighty per cent.? 
If the amount is near the dew-point, the air is moist ; if 



THE MOISTURE OF THE ATMOSPHERE 233 

the relative humidity is low, it is dry. Air that is moist 
at ;i given temperature may feel very dry at oik; that is 
higher, even though no more moisture is present. 

Latent Heat of Evaporation. — Water is changed to 
vapor by heat. When water boils it roaches the tem- 
perature at which it begins to change rapidly to steam. 
No matter how fierce the heat may he, the water (unless 
it is confined under pressure) gets no hotter, and the steam 
given oil" has a temperature no higher than that of the 
boiling water. 

All this heat is absorbed in the work of changing the 
water to steam, and it is called the latent heat of steam. It 
has not been lost, however ; it is merely stored-up energy. 
It is retained just so long as the water remains in the form 
of vapor; it is given out the moment the vapor is con- 
densed, or changes to a, liquid. 

This property of water is one of the greatest importance, 
for, as will he shown, it is a chief factor in the atmospheric 
disturbances called storms. The amount of heat thus ren- 
dered latent is very groat. For every pound of water con- 
certed to steam, as much heat is required as would raise 
nearly half a ton of water one degree F. 

Dew. Dew is the moisture that gathers on the ground 
after Sundown. Both the air and the ground lose a part 
of their heat. The latter cools more rapidly, however, 
and finally the layer of air next the ground is chilled be- 
low the dew-point. When this occurs, the excess of vapor 
in the form of minute drops gathers <>n the grass and on 
other objects near the ground. The moisture that gathers 
on the outside of a glass of iced water is an example. 

Dew does not always form at night, and for this there 

are several reasons. A stiff breeze may keep the air 
thoroughly mixed, and (hereby prevent anj pari <>f it 
from being chilled to the dew-point. The air may contain 



234 PHYSICAL GEOGRAPHY 

so little vapor that a fall of fifteen or twenty degrees does 
not bring the temperature to the dew-point. 3 A cloudy 
sky, especially if the clouds hang low, prevents the radia- 
tion of heat, and the formation of dew. 5 

The amount of moisture in the air varies much. In 
tropical regions, especially those near the sea, the amount 
is proportionately very great. Sometimes it is so near 
the point of saturation that the air becomes hazy. In 
such regions dew forms copiously. In temperate latitudes 
the amount is much less than in tropical regions. 

In the California and Sound valleys, where there are no 
summer rains, the fall of dew in early summer is excessive, 
and to a great extent the grain crop is dependent upon it. 
The same phenomenon occurs in mountain valleys of South 
America, of Asia, and of northern Africa. 

If the dew gathers on the surface of an object and there 
freezes, or if it freezes while in the air, and the minute 
crystals fall to the surface, frost is formed. A temperature 
of 0° (32° F.) or less is necessary to the formation of frost. 
Except at considerable altitudes frost does not occur in 
tropical regions. In temperate latitudes it may occur at 
any time between late fall and spring. Late spring frosts 
are apt to occur after fruit-trees have budded, and they are 
therefore commonly known as hilling frosts. The cold 
wave that follows a spring storm is very apt to lower the 
temperature to the freezing-point, and if the air be moist, 
a killing frost commonly occurs. Fortunately its occur- 
rence usually can be predicted 

Clouds. — When the temperature falls so low that a part 
of the vapor is condensed, the latter does not at first 
gather into large drops ; on the contrary, the drops are so 
minute that they float in the air. This floating mist of the 
air is called fog or cloud, according as it is at the surface 
of the earth or high in the air. 



THE MOISTURE OF THE ATMOSPHERE 235 



Nearly always the air is filled with dust-motes and other 
floating matter, and much of the condensing vapor gathers 
on these. Not only do the dust-motes form a lodgement 
for the condensing vapor, but they cool more rapidly than 
the air, aud thereby quicken the process of condensation. 
Floating matter in the air thus becomes an active agent in 
cloud formation. The cooling of the air below the dew- 
point, however, is the essential, and this may occur in 
several ways. Thus, when a mass of air is pushed upward, 
not only is it chilled by going into a cooler position, but 
it is also cooled by its own expansion. It is probable 
that the greater amount of cloud is formed in this manner. 
Thus, in equatorial regions, 
where there is a constant 
up-draught of warm, moist 
air, there is a perpetual 
cloud-belt. 

The intrusion of warm 
winds into cold regions, or 
of cold winds into warm re- 
gions, is also a common 
cause of fog and cloud. If 
the intruding wind is at the surface of the earth fog 
results ; if at a considerable elevation cloud is formed. 
The fogs and cloud banks so common off the coast of New- 
foundland are formed in this way. 

Whenever a warm sea-wind blows against a high moun- 
tain-slope, a part of the air is driven up the slope, and, 
some of its moisture being condensed, cloud is formed. 
Almost always high mountain-crests near the ocean are 
shrouded in clouds, and not infrequently a cloud banner 
streams from the leeward side of a high peak. 6 

Clouds usually take characteristic forms, and these are 
governed mainly by the presence or absence of wind, or by 




CIRRO-STRATUS CLOUDS 



236 



PHYSICAL GEOGRAPHY 



their height. Cirrus clouds are light and feathery in ap- 
pearance and commonly white in color. These clouds take 
various forms. When they are flaky or fleecy they are the 
" mackerel " clouds heralded by sailors as forecasters of flue 
weather ; but cirrus " streamers " are frequently found as 
an advance indication of an approaching cyclone. Often 
the patches of cirrus cloud are ranged in parallel strips ; 
and occasionally they radiate like the spokes of a wheel. 






CUMULUS CLOUDS 



Commonly their altitude is between Ave and ten miles. 
On account of their great height it is obvious that they 
consist of minute ice crystals. Cirri may form above 
another cloud, the two being apparently related, but they 
never form under other clouds. 

Cumulus clouds are the day clouds of summer weather. 
They appear like great, rounded domes resting on a hori 
zontal base. A gently warmed current of air rises until, 
being chilled both by expansion and great altitude, con- 
densation begins. The process continues until a dense 



THE MOISTURE OF THE ATMOSPHERE 237 



mass of cloud is formed. This form is the almost univer- 
sal cloud of tropical regions. It is abundant in warm 
temperate climates, but rare in cold latitudes. It does not 
form at night nor in cold weather, for the simple reason 
that the up-draught of warm air is too feeble, and there is 
not enough vapor present to form clouds of sensible dimen- 
sions. Ordinarily, cumulus clouds have no especial sig- 
nificance as weather forecasters. They indicate nothing 
more than the presence of moisture, and, as a rule, their 
size shows whether there is considerable vapor or only 
a little. If, however, a mass of cloud loses its flat base, 
becoming ragged or festooned at the lower side, it usually 
portends high winds and local showers. 

Stratus clouds are so called because they are flat layers 
of nearly uniform thickness. Normally they are the low- 
est of all clouds, and probably contain the greatest amount 
of foreign matter. These 
clouds are commonly ob- 
served at morning and even- 
ing, and stillness of air is 
essential to their formation. 

The Nimbus is the shape- 
less rain-cloud that hovers 
near the surface of the earth. 
The upper part consists of 
light fog or mist; the lower, 
of falling drops. Usually it seems to form in clear air, and 
it gathers when the temperature reaches the dew point. 

Clouds are moved hither and thither by the wind, but 
the matter composing the cloud is usually in motion even 
when the air is still. A casual inspection of any summer 
cloud shows that it is constantly moving within itself. 
Practically, cloud is floating moisture, but in reality the 
minute drops are always slowly falling. The droplet falls 






«*$*?**>. 



STRATUS CLOUDS 



238 PHYSICAL GEOGRAPHY 

until it reaches a region of greater warmth ; then it is 
changed to vapor, and the latter at once ascends until it is 
again condensed — the process being constantly repeated. 

Rain. — The difference between rain and cloud consists 
very largely in the size of drops, but there is also a differ- 
ence in their physical condition. The drops of cloud 
matter, or " water dust," are minute, and practically they 
float in the air; those of rain are each many thousand 
times as large, and fall quickly to the ground. The causes 
that operate to produce fog and cloud, however, also pro- 
duce rain — namely, the cooling of water vapor below the 
dew-point. 

The vapor precipitated as rain may pass through the 
cloud stage, it is true ; but the latter is one of short dura- 
tion, and, as a rule, when condensation begins, it proceeds 
very rapidly. Rain is rarely associated with fair-weather 
clouds, and, excepting local showers, is not derived from 
them. In almost every instance general rains are derived 
from warm ocean winds that, blowing inland, are chilled. 

The rainfall is greatest where evaporation is most rapid, 
and this is in the tropics. The equatorial cloud-ring is 
also a rain-belt, and under it precipitation is almost con- 
tinuous. The amount of rain falling in the torrid zone 
is sufficient to cover it to a depth probably of more than 
one hundred inches. In the temperate zone it is a little 
more than one-third, and in polar regions about one-eighth 
as much. 

Rainfall is not uniform for all places in the same lati- 
tude. 9 On slopes that face ocean winds it is greatest, 
while in regions shut off from the sea by high ranges it is 
little or nothing. For example, on the southern slope of 
the Himalayas the precipitation varies from two hundred 
to six hundred inches ; on the north side it is less than 
ten. On the western slope of the Sierra Nevada and Cascade 



240 PHYSICAL GEOGRAPHY 

Ranges it is ten times as great as on the eastern. Explain 
why the difference exists. 

As a rule, precipitation is greatest at the coast and de- 
creases toward the interior. 12 On the Atlantic coast of 
the United States it is nowhere less than forty inches ; 
west of the one hundredth meridian it is less than fifteen. 
On the northern shores of South America it is over one 
hundred inches ; a few hundred miles inland it is about 
one-quarter as much. In the uplands of the eastern slope 
of the Andes it again increases ; why ? 

Not only does the amount "of rainfall vary in different 
localities, for the reasons noted, but there is also much 
difference in the time of its distribution. In some local- 
ities it comes in the form of occasional showers ; in others 
long periods of rain and drought alternate at given inter- 
vals u — that is, the rainfall is periodical and seasonal. 

An examination of the wind chart, p. 221, will help to 
explain this fact. The slopes of the continents that face 
ocean winds, as a rule, have periodical rains. Thus, the 
western coast of North America faces the Prevailing West- 
erlies of the Pacific Ocean. In summer these winds are 
blowing into a region that is warmer, and therefore but 
little rain falls. In winter, on the other hand, the temper- 
ature of the land is much lower, and therefore rain may 
be of daily occurrence. 

On the Mexican coast, where, on account of low latitude, 
the climate is almost always mild, but little rain falls. 
Along the coast of the United States it varies from ten or 
twelve inches at San Diego to sixty or seventy at Puget 
Sound; while at Sitka, Alaska, it is about one hundred 
inches. How will the difference in* latitude explain this ? 
In what part of the Pacific Coast of South America are 
the conditions similar ? On the Atlantic coast of Europe 
the conditions are much the same ; most of the precipita- 



THE MOISTURE OF THE ATMOSPHERE 241 

tion occurs during the winter months, but on account of 
high latitude a considerable rain falls in summer. 

In tropical regions, where the winds have an easterly 
origin, the easterly slopes receive the heaviest fall of rain. 
In these regions, however, the rainfall follows the passage 
of the equatorial cloud-belt back and forth. This belt is 
comparatively narrow — scarcely five hundred miles in 
breadth. During the spring months of the Northern 
Hemisphere it moves northward with the sun, deluging 
the land over which it passes with almost continuous rain. 
After reaching its northern limit it turns southward, re- 
passing over the same belt. In the American continent 
the cloud-belt does not pass far south of the equator ; in 
Africa it reaches much farther south. 

A moment's study will show that at each tropic, or limit of 
the cloud-belt, there will be one rainy and one dry season, 
while at intervening latitudes there may be two. Which 
of these conditions applies to Cuba? to the Central Amer- 
ican states ? to the Caribbean coast of South America ? 

Regions swept by monsoons usually have periodical 
rains also. The reason is obvious : during one part of the 
year the winds blow from the land ; the remaining time 
from the sea. The rains of the Indian coast of Asia are 
an excellent example. During the winter months of the 
northern hemisphere the prevailing winds are land winds ; 
but with the bursting of the April monsoon the season of 
heavy rain begins and the parched land is quickly covered 
with verdure. 

A large part of the land surface of the earth is watered, 
not by seasonal and periodical rains, but by the pre- 
cipitation that comes with the irregular movements of the 
atmosphere known as storms. These regions as a rule are 
either far inland, or else high mountain ranges shut them 
oil* from the reach of ocean winds. 



242 PHYSICAL GEOGRAPHY 

That part of the United States east of the Rocky 
Mountains is an example. The ranges of the great high- 
lands precipitate practically all the moisture brought from 
the Pacific, and therefore there are no periodical rains. 
Moisture gathers from the Gulf and also from the ocean, 
but for the greater part it is not precipitated until the 
cyclonic movement, which constitutes the storm, takes 
place. These disturbances occur so frequently, and there 
are so many of them, that almost every part of the region 
receives a plentiful supply of moisture. Similar con- 
ditions exist in parts of Eurasia and Africa. 

Effects of Altitude. — As a rule, more rain falls at sea- 
level than at higher altitudes : very little falls above the 
height of ten or twelve thousand feet. On mountain - 
slopes, however, the greatest precipitation takes place be- 
low three thousand and five thousand feet. The reason is 
two-fold. In moderately warm regions rain clouds com- 
monly do not reach much above this altitude ; moreover 
at this height the ground may be cold enough to condense 
moisture when it is too warm to do so at a lower level. 
This fact is often observed in desert regions. 

Rainless Regions. — There are two principal causes 
for the existence of rainless regions. There may be a 
barrier of high mountains that shut off rain-bearing winds; 
or, vapor may pass into a warmer region where it cannot 
be condensed. The Basin Region of the western high- 
lands, the basin north of the Himalaya Mountains, and the 
Andine desert, are examples showing the effects of moun- 
tain barriers. The mountains reach higher than the rain 
winds. The two African deserts and much of the Mexican 
coast show the effects of hot inland regions. The ocean 
winds that penetrate these regions are warmed and not 
cooled, and therefore they are relatively drier. 

Snow. — When the condensing vapor freezes before it 



THE MOISTURE) OF THE ATMOSPHERE 243 

call gather into drops, snow results. It is evident, more- 
over, that snow cannot form unless the temperature is as 
low as 0° (32° F.). If condensation takes place very 
slowly in still air, the frozen droplets aggregate into beau- 
tiful crystalline forms, 1 - but if condensation is rapid, each 
Hake is a tangle of broken crystals. 

Inasmuch as snow depends on a low temperature, it is 
evident that the distribution is governed both by latitude 
and altitude. In polar regions snow covers the ground 
the greater part of the year, and at a little distance from 
the sea it never melts. In equatorial regions the line of 
perpetual snow is about sixteen thousand feet above sea- 
level ; in temperate latitudes it varies from seven thousand 
to twelve thousand feet. 

Hail. — Hail consists of pellets of ice, formed in the air, 
and a shower of them constitutes a hailstorm. Usually a 
hailstorm consists of alternate shells of snow and crystal- 
line ice. 13 In some instances sharp, dog-toothed crystals 
of ice project from the outer surface. Hailstones vary 
in size from tiny pellets to masses an inch in diameter. 
Larger stones occur, but they are formed by the cohesion 
of small ones. Hailstorms are more frequent in warm 
weather than in cold. For reasons unknown certain local- 
ities are especially subject to them. They very frequently 
accompany thunderstorms. 

QUESTIONS AND EXERCISES.— Find the annual rainfall of the 
neighborhood in which you live by striking an average of the yearly 
precipitation for at least ten years. {The statistics may be learned from 
the nearest Weather Station.) 

Make a record of the early and late frosts for the year. What fruit 
crops are injured by killing frosts in the neighborhood in which you 
live ? 

Learn, from the nearest Weather Station, the months in which the 
greatest amount of rain or snow falls ; — the least. 

What crops or plants of commercial value would suffer or perish 



244 PHYSICAL GEOGRAPHY 

if the rainfall in the State in which you live were decreased one- 
third ? 

Note the character and kinds of cloud visible during several days ; 
at what time were stratus clouds visible ? 

Explain how smoke may gradually gather cloud matter. Why is 
this most apt to take place toward evening ? 

The receiver of a rain gauge is a cylindrical cup four inches in diame- 
ter. For convenience of measurement the water caught is poured into 
a glass tube one inch in diameter : a depth of one inch of rain in the 
receiver will make how many inches in the tube ? 

Explain how a crust forms on the surface of snow. 

At a convenient opportunity, catch flakes of snow on a piece of black 
cloth ; examine them with a magnifying-glass and make drawings of 
their shapes. (Observe the conditions noted on p. 243.) 

COLLATERAL READING AND REFERENCE 

Tyndall. — Forms of Water. 

U. S. Weather Bureau. — Monthly Weather Review. Mid- 
summer and midwinter issues of any year. 

Greely. — American Weather— pp. 77-81, 134-162. 
Waldo. — Elementary Meteorology— pp. 142-165. 



NOTES. 

1 The expressions "air absorbs water in the form of a vapor " 
and "warm air can hold more water vapor than cold air " are so 
popular that ordinarily they pass for scientific truths. They are 
certainly convenient, but a moment's reflection shows them to 
be inexact. 

2 The phenomenon popularly known as "the sun drawing 
water " is due to the passage of rays of light through rifts in the 
clouds. The passage of the rays is marked by minute dust-moats, 
which reflect and scatter some of the light. 

3 At times it may be noticed that wet clothing exposed all day 
to the air refuses to dry. The reason is that the air is already 
saturated, and because of this no further evaporation can take 
place. 

4 Sometimes dew forms copiously with but a slight fall of tem- 
perature, while perhaps on a following night, none may appear, 



THE MOISTURE OF THE ATMOSPHERE 245 

though the temperature is much lower. An inspection of the 
table on p. 380, will explain how this may occur. If there were 
seven grains of water vapor in each cubic foot of air, a fall of 
temperature from 68° (F.) to 64° would be attended with dew ; 
but if only three grains were present, the thermometer might 
sink as low as 40° without any sign of dew. 

'" A cloth screen within four or five feet of the ground will have 
the same effect. 

6 These cloud banners were noticed in the Alps by Professor 
Tyndall, and were first described by him. They may be often 
seen streaming from the summit of Tacoma, Washington, and 
the alleged smoke from the 
crater of Mount Hood, Oregon, 
is nothing but a similar phe- 
nomenon. 

7 This indication has had a 
recognized place in weather- 
lore for two thousand years. 
It is mentioned in Virgil : 

Tenuia . . lanje per coelum val- 

lera ferri, 

MACKEREL SKY 

and it is found among Teutonic peoples, as well ; hence the 
popular saying — 

Mackerel sky, twelve hours dry. 

8 Not infrequently a column of smoke, from a factory chimney 
or a steamer's smoke-stack, becomes the nucleus of a stratus 
cloud. The smoke ascends until buoyancy and gravity balance 
each other, and then settles in the form of a thin, flat layer. 
Each particle becomes a surface of condensation, and the cloud 
matter continues to gather until it is swept away by the wind, 
or the conditions are changed. 

° The heaviest annual fall is probably at Cherrapunji, India, 
where the average is about 500 inches. In August, 1841, the total 
fall for the month was 264 inches, and in 1861 the yearly fall 
reached the enormous amount of DOS inches — about 2.5 inches a 
day ! On June 14, 1876, 40.6 inches fell in twenty-four hours. 
In the three days ending February, 189:}, an aggregate of 35.8 




246 PHYSICAL GEOGRAPHY 

inches fell at Brisbane, Australia. In the United States 21.4 
inches fell at Alexandria, Louisiana, in one day, and at Triadel- 
phia, West Virginia, 6.9 inches fell in fifty-five minutes. All 
these instances, however, are very unusual. Commonly, not 
more than two inches fall in a day. 

10 The greater the distance from the coast the more abnormal 
is the character of the rainfall. In the Basin Region of the west- 
ern United States, the rain is restricted to showers of short du- 
ration, and these often take the form of cloud-bursts. There is a 
sudden darkening of the sky, a terrific downpour of water — 
perhaps three or four inches in fifteen minutes — and then the sun 
is again licking up the water from the almost hissing rock waste. 
The specific cause of cloud-bursts is not known. 

11 In regions visited by periodical rains, not infrequently the 
air is so loaded with dust, at the end of the dry season, that the 
first rain is discolored and even muddy. The yellow and golden 
rain, once a great mystery, is commonly due to the pollen of 
pine. Examined under a microscope the character of this pollen 
is such as to leave no doubt as to its origin. Showers of frogs, 
fishes, and angleworms (!) have been reported, but not an in- 
stance has been substantiated. It is not impossible that a water- 
spout might whirl a school of fishes into the air, and then over 
the land, but no tornado known has been so selective as to con- 
fine itself exclusively to frogs and angleworms. The latter sim- 
ply emerge from their hiding-places at the onset of the shower. 
Among other abnormal showers are the rains from cloudless skies. 
Instances are common, especially in mountainous localities. The 
precipitation in such cases is very slight and the showers rarely 
cover more than a square mile or two. The sky is cloudless 
merely because there are not enough drops in the air at any 
moment noticeably to interrupt the light. 

12 With one or two exceptions all the illustrations of snow 
crystals are copies of drawings made in the arctic regions by 
Captain Scoresby. A few drawings have been made by Professor 
Tyndall, and recently excellent photographs have been obtained ; 
these show that ice-crystals and snow-flakes are not so regular 
nor so complicated in structure as those observed by Scoresby. 
In order to obtain good specimens of crystals, they must be 
gathered on a perfectly still day when the temperature is several 
degrees below the freezing-point. It is best to catch them on a 



THE MOISTURE OP THE ATMOSPHERE 247 

piece of black cloth, and if they are to be examined under a mi- 
croscope the glass slide on which the Make rests should be covered 
with the same material. The crystalline forms observed in sun- 
shine are materially different from those found in cloudy weather. 
13 The peculiar structm-e of hail-pellets has led to the theory 
that the stone has been whirled alternately into warm and cold 
layers of air; this is only a supposition, and concerning their 
formation nothing certain is known. As a theory, however, it is 
not unreasonable. Ordinarily, hail-storms are of only a few 
minutes' duration, and the amount falling is a small fraction of 
an inch in depth. In 1888, at Moradabad, India, hail fell to a 
depth of several inches, and in one district two hundred and 
thirty-five people were killed. In June, 1879, a storm swept over 
central New York and Massachusetts, during which stones seven 
inches in circumference fell. In July, 1880, a hail-storm destroyed 
the crops in the vicinity of Waupaca, Wisconsin. The shower 
covered an area of forty square miles. Stones from six to ten 
inches in circumference fell. In July, 1881, the fall of hail at 
Cumberland, Maine, was so great that drifts two feet deep were 
observed twelve hours afterward. In June, 1882, at Dubuque, 
Iowa, stones weighing twenty-eight ounces were found. In 
August, 1883, at Gray, Iowa, the drifting hail covered the fence 
tops. In June, 1886, so much hail fell in Grand Forks County, 
Dakota, that it did not all melt for thirty hours. In a single 
storm that passed over a small area in Dakota, a quarter of a 
million acres of wheat were destroyed. 



CHAPTER XIV. 



THE MOISTURE OF THE ATMOSPHEEE. CYCLONIC 

STORMS 

Both on the land and at sea' there are regions of con- 
siderable area that normally are not swept by regular and 
constant winds. 1 On the sea these are the calm belts ; on 
the land they are regions from which the winds are shut 
off by mountain-ranges or disturbed by broad stretches 
of land. On the sea the shifting of the calm belts with the 
season brings various parts successively under the influ- 
ence of the regular winds. 
On land the regular winds 
usually exist as upper cur- 
rents, while at the surface 
the winds are local and vari- 
able ; the upper currents, 
moreover, are so high that 
they are too cold to contain 
much moisture. 

Such regions do not re- 
ceive seasonal rains. The 
land areas, in some instances, receive none at all, except from 
an occasional cloud-burst ; but in many cases a consider- 
able rainfall results from the movements of local winds. 
That part of the United States east of the Rocky Moun- 
tains is an excellent illustration. It receives no moisture 
directly from the constant winds ; yet about every part of 
it east of the 2,000-foot contour is so generously supplied 

248 




STRATUS CLOUDS DISTURBED BY 
AN UP-DRAUGHT 



CYCLONIC STORMS 



249 



with rain that it is one of the most productive regions 
of the world. 

Whenever a local wind occurs, one of two conditions is 
pretty apt to exist. Either there is an up- draught toward 
which the wind is blowing, or else there is a great accumu- 
lation of air from which the air is spreading outward. 
These local disturbances 



50 


N. HEMISPHERE 


50 


X^\ 


40 


rWyCj 


40 


30 


/Ty~*^ 


30 


20 


^5fe^ 


20 


10 


10 


^Joy«s 


10 


10 


EQUATORIAL CALMS 


-c^^* 


20 


/^t' 


20 


30 


YQrv 


30 


40 


v^p) 


40 


sn 


^-^\^y 


50 




S. HEMISPHERE 





constitute the condi- 
tions popularly known 
as storms. Moreover, in 
either case the move- 
ment of the air sooner 
or later develops into a 
whirl. The wind that 
blows toward an up- 
draught or a depression 
forms a cyclone; that 
which blows outward 
from a high bank of air, 
an anticyclone. These 
disturbances originate 
both on the land and at 
sea. They are usually 
indicated by a changing 
barometer ; hence a cy- 
clone is often described as an area of low barometer — or 
simply a "Low" — and the anticyclone, one of high ba- 
rometer. As a rule both the cyclone and the anticyclone 
are local disturbances, and therefore they are carried along 
by the great currents of the air, just as an eddy formed in 
a river is carried along in its flood. 

Cyclonic movements therefore travel eastwardly in low 
latitudes and westwardly in latitudes beyond the tropics, 
because these are the prevailing directions of the winds. 



NORMAL CYCLONE TRACKS 



250 



PHYSICAL GEOGRAPHY 



Because of this fact, when a cyclone has once formed, the 
track along which it is likely to move can be predicted 
with considerable accuracy. The direction of the whirl 
has been learned by experience : in the Northern Hemi- 
sphere it is opposite that of the clock's hands ; in the 
Southern Hemisphere, the reverse.* A knowledge of 
these facts enables the mariner to avoid a cyclone, and 
also to steer out of it when overtaken by one. 

Tropical Cyclones.— Tropical cyclones usually origi- 
nate within a few degrees of the equator. They are the 
hurricanes of the West Indies and the typhoons of the 
China Sea. The storm area extends over a surface vary- 
ing from a few hundred to 
more than a thousand miles 
in diameter. The preced- 
ing illustration, p. 249, shows 
roughly the track which, or- 
dinarily, one of them fol- 
lows. What is its direction 
in tropical latitudes ? in lati- 
tudes beyond the tropics? 
Note the direction of the 
whirl in each hemisphere. 
It rarely extends beyond the 60th parallel. 

The real beginning of the tropical cyclone is the dead 
calm that for a few days precedes the disturbance, for 
it is only when the air is in a state of rest that the 
necessary conditions can obtain. 3 The first essential con- 
dition is the overheating of the air next the sea — pre- 
cisely the same condition that formed the beginning of 
the desert whirl (p. 224). But while the stratum of air 
that causes the desert whirl is only a few hundred feet 
in height and involves a very small area, the atmo- 
sphere disturbed by the tropical cyclone is, perhaps, 



"STREAMERS" OF CIRRUS CLOUDS 
—THE FORECAST OF A CYCLONE 



CYCLONIC STORMS 251 

several thousand feet high and many thousand miles in 
extent. 

The longer the sun beats down on the glassy surface of 
the water the greater will be the energy of the storm when 
it begins. Moreover, there is one element present in the 
tropical cyclone that is not found in the case of the desert 
whirl — namely, the vapor of water — and this is the most 
important distinction between the two. Finally the equili- 
brium becomes so unstable that a slight up-draught of air 
occurs where the resistance is least. The moment this 
occurs, the rising air already near the dew-point is chilled 
by its own expansion, and a part of its moisture is precip- 
itated. The fall of rain sets free an enormous amount of 
latent heat, aud a furious up-draught at once takes place. 

It is the latent heat of the moisture set free that gives 
to the cyclone its great energy. This indeed is its fuel, 
and so long as the supply lasts, just so long will the cy- 
clone continue. The ascending air at first is very moist 
and tolerably warm. But after its moisture has been con- 
densed the latent heat set free renders it dry and very 
much warmer, thereby increasing the up-draught. 

The nearer the centre of the cyclone, the stronger is the 
wind. The "eye" of the storm, or the centre of the 
whirl, is the up-draught of the cyclone, and here brief in- 
tervals of sunshine alternate with torrents of rain. In the 
centre of the storm the barometer stands lowest — perhaps 
two inches lower than it is beyond the edge of the storm. 

The path of the cyclone seems at first to be one of un- 
usual shape, but when examined in relation to the prevail- 
ing winds the mystery disappears. It is not unlikely that 
the temperature of the upper air has much to do with the 
northerly tendency of the cyclone. Because cold air is rel- 
atively heavier than light air, the colder the upper air 
that surrounds the up-draught, the more vigorous will the 



252 PHYSICAL GEOGRAPHY 

latter be. In the Northern Hemisphere the colder air lies 
to the northward of the storm, and this will be the direc- 
tion of least resistance. 

Knowing the direction of the whirl and the path of the 
storm, it is not difficult to lay the course of the vessel out 
of the way of the cyclone. For this purpose " storm- 
cards," or diagrams similar to that on p. 263, are conven- 
ient. The distance of the storm-centre can be estimated 
only to a rough degree, but the .bearings can be obtained 
with a high degree of probability. Facing the wind the 
storm-centre is on the right hand. 4 

Winter Cyclones. — Some of the fiercest storms of the 
higher latitudes, however, do not originate anywhere within 
tropical regions. These are the extra-tropical or winter 
cyclones, and the fierce winter storms of the North Atlan- 
tic Ocean are examples. It is evident that these storms 
cannot originate in a dead calm, because there is no long- 
continued calm weather where they form ; and it is equally 
apparent that they are not formed by the overheating of 
the air next the surface of the water. 

It is thought that these storms result from the intrusion 
of cold, north winds into the region of warm and moist 
air, to the southward. In any case the condensation of 
moisture creates an up-draught that quickly develops into 
a whirl. But if, at the time of intrusion, the cold air takes 
the upper position, the equilibrium becomes much more 
unstable, and the storm very likely develops into one of 
great fury. 5 

Land Storms. — The occasional local squalls excepted, 
all the storms of the land are cyclonic in nature, and 
except in violence they do not differ materially from the 
cyclones of the sea. In nearly every case they follow the 
same courses that are taken by the latter — westerly in 
tropical and easterly in temperate latitudes. 



CYCLONIC STORMS 



253 



Since the establishment of the various weather bureaus, 
the storm-tracks have been closely studied, and it is found 
that most storms follow certain lines or belts. 

In the United States two storm -tracks are apparent. 
The lesser number follow the trend of the Atlantic coast. 
The storms usually overlap the shore and the coast plain, 
but they seldom extend west of the Appalachian highlands. 
These storms 
belong to the 
class of West 
Indian cyclones. 
They originate 
in the Caribbean 
Sea, and turning 
nort hward, 
finally reach the 
latitude of the 
Middle Atlantic 
coast. 

Most of the 
storms that pre- 
vail in the Unit- 
ed States form 
near the great 
highlands of the 
west — very fre- 




A STORM, OR AREA OF LOW BAROMETER 

The shaded part is the area of rain ; the dotted region the area 
of cloudiness. The arrows fly with the wind. 



quently near the 

eastern base of the Rocky Mountains, crossing the con- 
tinent in a northeasterly direction. These storm -tracks 
have a distinct tendency to shift north or south with the 
apparent motion of the sun, the belt being a little farther 
north in summer than in winter. The valley of the St. 
Lawrence River and the basin of the Great Lakes is a 
common track. 



254 



PHYSICAL GEOGRAPHY 



— IV % k O 



Although they are sometimes accompanied by local 
squalls, land storms rarely exhibit the fury of ocean 
cyclones. The area of the storm is usually larger, but 
the wind seldom attains a velocity greater than forty 
miles an hour. The storm-centre is distinct, but the 
barometer may not fall more than half an inch. 

Clouds, and rain or snow, accompany the majority of 
storms, but the area of rain does not always cover the 
whole extent of the storm ; as .a rule, most of the cloud 
area, and the rain as well, occur in front of the storm- 
centre. With the passage of the latter there are occasional 
hard showers in which the rain falls almost vertically, or 

perhaps drives slightly tow- 
ard the east. These are the 
" clearing showers." 

Because the wind blows 
toward the storm-centre, it 
is evident that storms of the 
second class will be pre- 
ceded by easterly and will 
clear with westerly winds. 
Those from the West Indies 
will begin with northeasterly and clear with southwesterly 
winds — the "nor'easters " and " sou' westers." 

In some instances general storms are accompanied by 
disturbances of a very violent character. Of these the 
most important are thunder-showers, cold waves, and 
tornadoes and waterspouts. Thunder-storms and torna- 
does are local in character, and often occur independently 
of general storms. Waterspouts and tornadoes are local, 
the former being confined to the water. Cold waves are 
general. 

Cold Waves. — Just as the trough of a wave of the sea is 
followed by the crest of another wave, so in the aerial 




CLEARING WEATHER CLOUDS 



CYCLONIC STORMS 255 

ocean an area of low barometer is followed by one of high 
barometer, and if the latter be an anticyclone of cold air the 
result is a cold wave. 

Not infrequently it happens that the barometer is con- 
siderably higher on one side of a storm-track than on the 
other. In such a case, it is evident that most of the air 
flowing in to till the depression will come from that side 
on which the barometer is the higher. If the air is drawn 
in from the south side, it is pretty apt to be a mass of 
warm, moist air, and the farther north the storm track, the 
higher in latitude will the body of warm air intrude. 7 On 
the contrary, if the bank of cold air lies to the northward, 
the depression will fill chiefly with cold air from this 
direction. 

In summer neither the cool air nor the warm air, follow- 
ing the passage of a storm, varies much more than eight or 
ten degrees from the usual temperature. In winter, how- 
ever, if the storm-track lies well to the south a large 
volume of very cold air will be drawn far to the south and 
the temperature may fall forty or fifty degrees in a day's 
time, or even in a few hours. 8 Ordinarily, the cold wave 
flows in not more forcibly than a brisk wind, but occa- 
sionally it advances with the force of a hurricane, lower- 
ing the temperature to thirty degrees or more below zero 
(F.). In such cases the cold wave is called a blizzard ° and 
it is marked by a furious downfall of snow. 

Tornadoes. — Tornadoes are whirling storms of the 
land. Though they cover a smaller area than any other 
storm, they are probably the most violent atmospheric 
disturbances known. 10 The path of the tornado seldom ex- 
ceeds thirty or forty miles in length, while the destructive 
part of the whirl is not more than a few rods in width. 
Like other cyclonic disturbances, the tornado is formed in 
an area of low barometer. Seen at a distance of one or 



256 



PHYSICAL GEOGKAPHY 



two miles, the tornado appears as a dense, black, funnel- 
shaped cloud hanging from rapidly whirling clouds above. 
The funnel is the centre of the storm, and so rapid is 
the whirl that it forms almost a vacuum. The rotatory ve- 
locity of the wind is thought to be not far from two miles 
a minute. 

Between the terrific wind and the vacuous centre noth- 
ing can withstand the force of- the tornado. The stout- 
est tree-trunks are twisted as though they were ropes, 

and in many instances 
pulled clear out of the 
ground. Buildings in 
the way of the funnel- 
cloud burst into pieces 
outwardly the moment 
the latter envelops them ; 
heavy locomotives are 
lifted from the railway 
track ; and iron bridges 
are blown from their 
foundations, twisted into 
shapeless tangles, and 
carried long distances. 
Another noticeable feat- 
ure is the lane or " wind- 
road " made when a tor- 
nado passes through a 
forest. 

A close study of sev- 

measure has shown the 

At the beginning of 




A TORNADO TRACK. 

The position and direction of the rails show the 
direction of the whirl. 



eral hundred tornadoes in a 

manner in which they originate. 

a storm it sometimes happens that a great volume of cold, 

dry air lies on one side of the disturbance, while a mass 

of warm, moist air lies on the other side. Such a con- 



CYCLONIC STORMS 



257 



ilition, indeed, is not infrequently the immediate cause of 
the storm. 

During the progress of the latter large volumes of cold 
air are whirled into regions of warm and moist air. Now, 
if the heavier cold air lies next the earth, no disturbance 
follows. But if it comes to rest on tin; top of a thick layer 
of warm air the case is different. The conditions are those 




A TORNADO AM) ITS 1-UNNHI. CLOUD. 



of unstable equilibrium, and the latter will sooner or later 
be upset. There results an up-draught of warm air, and 
soon the whirl is in full vigor. 

In about ninety-five per cent, of all the tornadoes 
studied the whirl accords with that of other storms in the. 
Northern Hemisphere. Almost always they move from the 
southwest to the northeast. 11 In nearly every instance 
thus far recorded the tornado track lies south of a general 
storm. 



258 



PHYSICAL GEOGRAPHY 



All parts of the United States are subject to tornadoes, 
but they are most prevalent in the central part of the Missis- 
sippi Valley. West of the 102d meridian they are extremely 
rare, because there is so little moisture in the atmosphere. 
There is also a belt south of the Ohio River, in which 

they are infrequent. They 
rarely occur in mountainous 
regions. 

Tornadoes are more frequent 
in summer than winter. The 
greatest number occur in May 
and more oc- 
cur in May, 
June, and 
July than dur- 
ing all the 
remaining 
months. They 
are more fre- 
quent in the 
afternoon 
than in the 
morning, and 
rarely occur 
at night. 
Waterspouts. — A waterspout is a whirlwind of the sea 
or other large body of water. The whirl is so rapid that 
the water is carried upward to fill the vacuous centre. The 
lower part of the waterspout is probably a nearly solid 
column of water ; the upper part is a rapidly whirling 
mass of spray. Waterspouts are most common in the 
region of cyclone tracks — especially along the track of the 
Gulf Stream. It is usually asserted that the water that 
composes them is fresh. This is not always the case, 




EFFECTS OF A TORNADO. 



CYCLONIC STORMS 259 

however ; in many instances it is salt — sea-water, pure and 
simple. In the lower part the column is not more than 
ten or fifteen feet in diameter ; in the upper part it is 
whirled into a balloon-shaped cloud of spray and mist 
several hundred feet in width. 

The white squall is similar iu origin to the whirl that re- 
sults in a waterspout ; iu fact, it ma}* properly be called a 
fair-weather whirlwind of the sea. It is sufficiently violent 
to whirl a considerable volume of sea-water into spray, 
but hardly strong enough to form a waterspout. 

Weather Forecasting. — Knowing the laws of storms 
and normal atmospheric movements, it is not a difficult 
matter to predict weather conditions with considerable 
accuracy. In the temperate zones weather conditions 
originate to the westward or southwestward of the ob- 
server ; in tropical regions, they progress from the east- 
ward. 

Except in the extreme southern part, where disturbances 
are occasionally tropical in their movements, the weather of 
the United States is essentially of the westerly type. That 
is, all disturbances progress from the west or southwest 
to the east or northeast. 

The United States Weather Bureau 12 was organized 
for the purpose of protecting agriculture, navigation, 
and commerce by furnishing information of coming storms, 
dangerous coast-winds, threatening floods, cold waves, and 
killing frosts. Scattered over the whole territory in 
selected locations are upwards of six hundred observers 
who, twice a day, at the same actual time, observe tem- 
perature, barometric pressure, relative humidity, direc- 
tion of wind, amount of rain or snow, etc. These re- 
sults are telegraphed to Washington and entered upon a 
weather map. 

Lines are drawn through localities of equal barometric 




STORM CENTER: FIRST DAY 




STORM CENTER : SECOND DAY 



CYCLONIC STOEMS 261 

pressure, and also through localities having the same tem- 
perature. The former are isobars, the latter isotherms. 
In this manner areas of high, normal, and low barometer 
are readily mapped and located. When the direction of 
the wind is plotted it will be found that it is everywhere 
blowing toward the area of low barometer. 

Twelve hours afterward, when a new set of observations 
is plotted, it will be found that the area of low barometer 
has advanced eastward with about the velocity of an or- 
dinary express train. With this information both the 
direction and the velocity of the storm can be quite ac- 
curately forecast for the succeeding twenty-four hours. 
Practically all general storms begin with easterly and clear 
with westerly winds. 

About ninety per cent, of the predictions may be verified 
and the number actually verified is very close to the possi- 
ble limit. Failure of verification is due to several causes — 
the sudden swerving of a storm from its track, the dissipa- 
tion of a storm once formed, and the unforeseen develop- 
ment of a local storm. The shifting of a storm one hun- 
dred miles on either side of its predicted track may nullify 
the forecasts over a very large area. 



QUESTIONS AND EXERCISES.— Why does the wind blow toward 
a low and away from a high barometer ? 

Why do cyclonic movements of the wind move toward the west in 
tropical, and toward the east in temperate latitudes ? 

Why does the water flowing out of a sink through a discharge-pipe 
at the bottom form a whirlpool ? 

In the map at the top of p. 260, near what city is the centre of the 
storm ? What is the direction of the wind at New Orleans and Baton 
Rouge? — at St. Louis and Cairo?— at Chicago and Davenport? — at 
Duluth? — at Cheyenne? — in the greater part of North and South 
Dakota ? 

Name one or two places at or near which the barometer is 29.5 inches; 
29.7 inches ; 29.9 inches ; 30 inches. 



262 PHYSICAL GEOGRAPHY 

About how far has the storm advanced at the time of observation on 
the second day ? 

Note the direction of the wind at Pittsburgh, Cleveland, Wilming- 
ton, N. C, Cincinnati, Indianapolis, Chicago, Springfield, 111., Mil- 
waukee, New Orleans, Mobile and Little Rock. 

The wind whirls warm, moist air from the south to colder, northerly 
latitudes ; what will be the effect on the moisture ? — on the temperature 
of the region over which the storm passes ? 

In what position, with reference to the storm centre, is most of the 
rain, as indicated by the shading ? 

Whence comes the air in the western part of the whirl — from 
northerly or from southerly regions ? 

Will it probably be colder, or warmer ? Why ? 

Make a forecast for Cincinnati for each of the two days. 

Make forecasts for New York, Denver, and Chicago for the third day. 



COLLATERAL READING AND REFERENCE. 

Greedy. — American Weather— pp. 178-272. 

United States Weather Bureau. — Daily Weather Maps. 



NOTES 

1 In the tropics the cloud-ring rarely exceeds five hundred miles 
in diameter, and the circle of dangerous winds is scarcely more 
than half as great. In higher latitudes, however, the diameter 
of the storm increases. The wind is more violent in tropical, 
and less severe in higher latitudes. 

3 The direction of the whirl is thought to result from the con- 
flict of winds as they approach the up-draught. Of all the cur- 
rents setting toward the storm-centre, the northeast Trade Wind 
is the strongest. As it approaches the storm-centre it is opposed 
by weaker winds from the north, northwest, and west. As a re- 
sult, the Trade Wind is bent toward the east and forced to rotate 
in the manner described. 

8 The barometer gives first warning of the approach of the cy- 
clone. During the few days preceding, the barometer is perhaps 
above its normal height and the weather pleasant and clear. 
Sooner or later the barometer begins to show signs of unsteadi- 



CYCLONIC STORMS 263 

ness, and at the same time a long, low, ocean swell becomes per- 
ceptible. Possibly a streamer or two of cat-tail clouds pointing 
toward the zenith is seen in the south or southwest, and a Avhit- 
ish arc near or on the horizon indicates the bearing of the cen- 
tre. In a few hours or less the barometer begins to fall — slowly 
at first, and then more rapidly. A halo gathers around the sun 
or the moon ; the ocean swell increases, the sky grows purple, 
and fitful puffs of wind come from the north. There can no 
longer be any doubt of the approaching storm, and the prudent 
master has already made everything snug and ready for the com- 
ing blow. Soon a heavy, mountainous bank of cloud looms up 
from the horizon. This is the cloud-ring that marks the edge of 
the storm, and the circle of dangerous winds is not far away. 
Finally the wind, already very squally, bursts into a gale, and 
veers to the northward, and soon the storm is on, in full force. 
If, by any means, the course has not been altered, or if, through 
accident, the ship is carried with the wind, the latter will in- 
crease to hurricane strength, and not even the smallest storm- 
sail will stand against its force. Soon, in almost a twinkling, 
the wind lulls and the ship is in the eye of the storm. Then the 
sky alternates between inky blackness, with terrific down-pours 
of rain, and moments of misty, yellow light. Perhaps half an 
hour passes, and the opposite side of the cyclone strikes the 
vessel. At that moment the wind again bursts upon the 
ship from the opposite direction. Nothing but the stanchest 
vessel can ride through such a storm. A square-rigged ship is 
apt to have her yards stripped off, even if the masts are not 
snapped. 

4 The accompanying storm cards are adapted to use in any 
cyclones of the northern hemisphere ; the upper diagram is 
available for the route between New York and English ports. 
The small arrows fly with the wind ; the long arrow represents 
the storm track through the belt of latitude to which the dia- 
gram applies. For West Indian hurricanes note that the storm 
track recurves as follows : June and October, latitude 20° to 23°; 
July and September, latitude 27° to 29° ; August, latitude 30° to 
33°. When a falling barometer and other signs indicate the ap- 
proach of a cyclone, select the diagram that applies to the lati- 
tude and plot the position of the ship according to the direction 
oi the wind. In low latitudes, for instance, the wind is N NE ; 



264 



PHYSICAL GEOGRAPHY 




the vessel is then in the position that is shown on the lower 
diagram, and is in the dangerous semicircle. If possible it is 
best to lie-to (on the starboard tack), and observe the wind ; if 
(a) it freshens without shifting, the vessel is certainly in the 
storm track. In this case the navigator keeps off, with the wind 
on the starboard quarter, holding to the course. (/>) If it shifts 
to the right, the ship is to the right of the storm track and should 

be put on the starboard tack, 
.,£&?/■> <s i=r ^ es ^, making as much headway as 
possible until obliged to lie-to. 
(c) If it shifts to the left, the 
ship is on the left of the storm 
track and sbould be brought 
about until the wind is on the 
starboard quarter, lying-to on 
the port tack if necessary. . In 
scudding, the wind sbould be 
kept always on the starboard 
tack to run out of the storm. 
If the vessel is in the latitude 
where the cyclone probably 
recurves (according to the 
month) the middle diagram is 
applicable. Suppose that the 
wind is S E ; the vessel then 
has the position marked in 
the middle diagram. It is on 
the right of the storm track 
and should run out as in (b), 
previously noted. In high lat- 
itudes the upper diagram is 
indicated. Suppose that the 
wind is N E. The ship then has the position shown to the left 
of the storm track, in the navigable semicircle, and should be 
brought about as in (c), previously noted. In any case oil may 
be used to prevent the waves from breaking over the vessel. 

It is unstable because the cold air is resting on a layer of 
air that is specifically lighter, and when the latter is pressed up- 
ward it soon develops into a whirl. Winter cyclones are not 
confined to definite localities, as are tropical cyclones, and in 



flW 

f ys sw. 



"VT* ii< 



'SW. °AHGEfi 0l 

ME /E«F, E. "8 

N i NE - sy, e^r <S=r s* 

Mb <#^ * 




\ ^0 % ''I 

S\t 8W. /8 SW. 

STORM CARDS. 



CYCLONIC STORMS 265 

comparison with the latter their trucks are erratic. Their gen- 
eral direction is easterly, however. 

1 In very many cases a land-storm may originate at sea and 
finally end somewhere at a considerable distance inland. Many 
West Indian hurricanes sweep into the Gulf of Mexico and thence 
into the Mississippi valley. On the other hand, there are many 
— perhaps a majority of north Atlantic storms — that begin far in 
the interior of the continent. In many instances storms have 
originated somewhere in the Pacific, crossed the United States, 
and the Atlantic, finally disappearing in the interior of Eurasia. 
Many of the cyclonic storms of the Pacific Coast of the United 
States travel southward between the Coast Range and Sierra Ne- 
vada Mountains. In some instances the storm is dissipated in 
the arid region to the southward, but occasionally a cyclonic 
disturbance tinds enough moisture to enable it to pass into the 
Mississippi Valley. 

1 Under such conditions a warm wave results. Although with 
respect to temperature, the difference between warm waves and 
normal weather is not so great as that between cold waves and 
normal weather, yet the former are far more fatal. In all the 
densely populated parts of the country the advent of a warm 
wave is marked by an enormous increase in the death-rate. Dur- 
ing several warm waves that, in July, 1881, covered the Missis- 
sippi Valley, there were more than one thousand deaths from 
sunstroke — probably a greater number than have resulted from 
the cold waves of a score of years. Warm spells may result from 
other cases. The typical " warm wave " is the result of settled 
conditions, and not disturbances. The air resting upon the given 
area without being disturbed in the course of two weeks becomes 
intolerably hot. 

8 A cold wave that occurred in January, 1S88, is an example 
of the effects of the translation of cold air from the extreme 
north. At Helena., Montana, the temperature fell fifty degrees 
in four and one-half hours, and sixty-four degrees in less than 
eighteen hours. At Crete, Nebraska, the thermometer fell eigh- 
teen degrees in three minutes. This wave covered almost the 
Whole United States, carrying freezing weather into Florida, 
California, and southern Texas. In March, 1887, a cold wave, 
extending along the valley of the St. Lawrence River, was 
marked by a fall of temperature ranging from fifty to seventy- 



266 



PHYSICAL GEOGRAPHY 



one degrees in twenty-four hours. In Denver, January 15, 1875, 
there was a drop in temperature of forty- eight degrees in one 
hour. 

' This term was first noted in the records of an exploring party 
which, in 1747, wintered on the shores of Hudson Bay, at a place 
now called York Factory. It was introduced as a technical name 
into the weather service in 1876. 

10 General A. W. Greely, U. S. A., notes twenty-five tornadoes, 
in which the aggregate damage reached the sum of $15,000,000, 
while the loss of life was nearly fifteen hundred. Concur- 
rent with a storm that in February 9, 1884, crossed the United 
States, there were sixty distinct tornadoes. On that day eight 

hundred people 
were killed, twen- 
ty-five hundred 
were wounded, 
and more than ten 
thousand build- 
ings were de- 
stroyed. 

"The story il- 
lustrated in this 
cut is a grewsome 
summary of hor- 
rors. The house 
was surrounded 
by a grove of trees. 
To the east of the house the trees were felled and twisted from 
right to left ; those west of the house were untouched. The 
house itself was demolished and the debris hurled into the creek- 
bed near by. When the tornado cloud swooped down upon the 
house, the family fled for their lives, but unfortunately in the 
wrong direction. At first they ran northward, a direction of 
safety. Then, one after another, they turned eastward — first a 
little girl, who was instantly killed ; then an older boy and a 
girl, who were bruised and partly stripped of their clothing. 
The mother ran directly into the whirl and was found crushed 
and mangled against the trunk of a tree. The father, with the 
babe in his arms, had reached a place of absolute safety, but in 
his fright turned eastward and ran into the whirl. They were 




CYCLONIC STORMS 267 

picked up by the wind, thrown several hundred feet, and instant- 
ly killed. An inspection of the accompanying illustration 
shows that the safest path of flight is toward the northwest or 
the southeast ; to the southwest or the northeast is one of the 
greatest danger. 

12 In 1853 the necessity for a weather bureau was urged by 
Commander M. F. Maury, but it was not until after his death 
that systematic land observations were carried out. The first 
organization was effected by General Myer, U. S. A., Chief Signal 
Officer, who trained the rank and file of his department to make 
weather observations. Since that time the Weather Bureau has 
been attached to the Department of Agriculture and placed in 
charge of its Secretary. Most of the European nations have es- 
tablished similar bureaus, and daily observations are made on all 
transatlantic steamships. So complete ai*e these records that 
scarcely a storm occurs in the North Atlantic which is not fol- 
lowed and its path predicted with a high degree of probability. 
Flags (or sometimes painted cylinders and cones) are displayed on 
public buildings in nearly every town in the United States and 
Europe. For land service these flags are commonly used. A 
square white flag denotes clear weather ; a blue flag, rain or snow. 
Temperature is indicated by a triangular blue flag. Above the 
square flag it denotes higher temperature ; below the square flag, 
lower temperature ; its absence denotes no change in tempera- 
ture. Whenever the temperature falls twenty degrees or more 
(sixteen degrees in the northern States) if the mercury sinks as low 
as 32° (F.), it is technically a cold wave, and its approach is indi- 
cated by a white flag containing a black square. It is commonly 
called the "black flag." A fifth flag is sometimes employed to 
indicate local storms. For the benefit of mariners a Monthly 
Pilot Chart for the North Atlantic is published by the United 
States Hydrographic Office. This shows storm tracks of the pre- 
ceding month, and the position of ice, fog, floating wrecks 
(called "derelicts"), and other obstacles, for the current month. 



CHAPTER XV 

ELECTEICAL AND LUMINOUS PHENOMENA OF THE 
ATMOSPHERE 

Electeicity is a form of energy that is manifested 
chiefly by its effects ; of its actual nature practically noth- 
ing is known. The laws pertaining to it are fairly well 
known, however; and, like most of the other forces of 
nature, it is a most useful servant when under intelligent 
control. In the slender thread of the incandescent light 
and the carbons of the arc light it appears both as light and 
intense heat. Passing through insulated copper-wire that 
surrounds a core of soft iron, it converts the latter into a 
magnet, and thus harnessed it becomes a generator of great 
power. Electrical energy seems to be a form of motion, 
and it may be produced by motion. It is manifest not 
only in the earth and the air, but in space as well. 

The fundamental laws of electrical energy are not diffi- 
cult to understand. If a pith-ball, suspended by a silk 
fibre, be brought near a piece of hard rubber, or vulcanite, 
that has been briskly rubbed by flannel, the ball will at 
first cling to the vulcanite and then immediately be re- 
pelled from it. If another ball, electrified in a similar 
manner, be brought near the first, the two will vigorously 
repel each other. 1 If, however, the second pith-ball be 
electrified by a piece of glass rubbed with silk, the two 
balls will then show a strong attraction for each other. 

Such an experiment demonstrates the principal laws of 
electricity. Bodies similarly electrified repel; bodies dif- 

368 



ELECTRICAL AND LUMINOUS PHENOMENA 269 

ferently electrified attract one another. The electricity de- 
veloped when glass is rubbed with silk is called positive ; 
that produced by rubbing vulcanite with flannel, negative. 
Electricity passes quite freely through metallic sub- 
stances, but with difficulty through such material as silk, 
wool, gums and resins, dry wood, and dry air. When, 
however, the electric force is so great that it will pass 
through these it is said to have a high potential, just as 
steam confined within a boiler is at high pressure. 2 The 




LIGHTNING 
From an instantaneous photograph by W. F. Cannon. 

"sparks" produced by rubbing sealing wax or vulcanite 
with flannel are of moderately high potential. 

To the electricity of the air and the earth many of the 
most marvellous phenomena are due. In the simplest 
form we see its effects when tiny sparks result from rub- 
bing the long knap of woollen cloth or the fur of an animal 
pelt ; we see its grandest effects when great flashes of light- 
ning forge across the sky. The electricity of the air is usu- 
ally of high potential ; that which forms a flash of light- 



270 PHYSICAL GEOGRAPHY 

ning is of exceedingly high tension. Next the earth, 
however, the electricity of the atmosphere is not commonly 
noticeable, especially if the air is moist. At considerable 
elevations, or at times when the air is very dry, its pres- 
ence becomes marked. The hair of the head crackles as 
a comb is drawn through it, and tiny sparks are given off 
when woollen clothing is rubbed. In the dry summer 
climate of deserts, the hair of horses' tails stands out like 
bushes, and their manes are like fright Avigs ; sparks half 
an inch long may be drawn from a metallic body insulated 
from the ground. 

Ordinarily the electricity of the air is positive, but, with 
much moisture present, it may be negative. Just before 
the beginning of a gentle shower it often becomes nega- 
tive, and during a heavy storm it frequently changes from 
positive to negative and vice versa very rapidly. In such 
cases the character of the electricity may vary in different 
places ; that is, it may be positive at one locality and neg- 
ative at another, only a few miles distant. 3 

Neither physical nor chemical change in a substance 
takes place without the development of electric energy. 
Friction likewise is a potent factor in its generation. The 
flowing of water ; the chafing of the winds against the 
earth's surface ; even the friction of the air against itself 
produces it copiously. Evaporation and condensation are 
attended by an electric disturbance ; and inasmuch as an 
enormous amount of the vapor of water is constantly aris- 
ing from the earth at one place to be condensed, 4 at an- 
other these changes in physical form, together with fric- 
tion, may be regarded as the chief agents in its production. 

Since these factors are constantly at work, it is evident 
that electricity is being constantly produced. But the 
electricity of the air and that of the earth are unlike ; 
the two, therefore, neutralize each other. Because moist- 



ELECTRICAL AND LUMINOUS PHENOMENA 271 

lire is a good conductor, if the air be moist the two kinds 
of electricity readily pass, one from the earth to the air, 
the other from the air to the earth, until the equilibrium 
is restored. This transference is quietly but constantly 
going on, so that ordinarily there is no great accumulation 
of electricity. It is only when the air is very dry that 
the transference takes place with difficulty. 

Thunder Storms. — When clouds are present in the 
air, however, there is often an enormous accumulation of 
electricity, either within or upon their surface, and the 
transference or exchange, therefore, may become violent 
and destructive. Such disturbances are commonly known 
as thunder storms. 

When large masses of cloud hover over the earth it 
sometimes happens that they are differently electrified. 
Under such circumstances the two clouds are mutually at- 
tracted. The potential of the electricity is very high and 
the transference takes place in the form of blinding flashes 
of lightning. 5 Usually the interchange takes place between 
the two clouds, but not infrequently it is between the 
clouds and the earth. The form of lightning varies. The 
interchange takes place always along the line of least re- 
sistance, and as this is seldom, if ever, a straight line, it 
has taken the name, zig-zag lightning. 6 

Another form is known as sheet lightning. This inter- 
change takes place, not along a line, in the form of a 
chain, but simultaneously over a large area. The dis- 
charge is not attended by a crash of thunder nor by a 
blinding flash of light. On the contrary there is nothing 
but a quivering, bluish glow that lasts sometimes for eight 
or ten seconds. A sheet-lightning discharge takes place 
usually between the earth and the clouds. The electricity is 
of low potential and therefore not destructive. This name 
is also applied to flashes of lightning that, occurring at 



272 PHYSICAL GEOGRAPHY 

a considerable distance, are reflected from tho under sur- 
faces of clouds. 7 Still another form is commonly called 
ball lightning. Of this kind of discharge but little is 
known, and although its occurrence has been alleged for 
more than two hundred years, its existence is somewhat in 
doubt. 

Occasionally the discharge takes unusual forms. Among 
them, but rare in occurrence, is the phenomenon known as 
St. Elmo's fire. This discharge, though best known at sea, 
is also occasionally observed on land. At the time of its 
occurrence there is usually a considerable electrical disturb- 
ance, though not necessarily a thunder-storm. Owing to 
the feebleness of the light emitted, it is rarely if ever 
noticed in the daytime. It consists of a pale, shimmering 
light, at the tips of the yards, spars, and from every 
pointed part of the ship's rigging. The glow lasts for a 
few moments and then the phantom light disappears. 8 In 
all probability the St. Elmo's fire is identical with the 
bluish glow that is seen when a frictional electrical 
machine is worked in the dark — a phenomenon commonly 
known from its shape as the " brush " discharge. 

The Aurora Borealis. — This magnificent display, 
commonly called the "northern lights," 9 is without doubt 
an electrical phenomenon that possibly is similar in nature 
to the brush discharge. It is most common in high lati- 
tudes, though it is occasionally observed between latitudes 
30° and 40° N. In appearance the aurora is an arch of 
light stretching across the sky fifteen or twenty degrees 
above the horizon. It has a tremulous motion, and the 
upper streamers sometimes mount to the zenith. 

In color the aurora varies between pale green and crim- 
son. Sometimes it closely resembles a green curtain edged 
and lined with gold. Auroras are most frequent during 
sun-spot periods ; they are usually coincident with mag- 



ELECTRICAL AND LUMINOUS PHENOMENA 273 

netic storms also. In circumpolar regions they aro of 
daily occurrence. 10 The cause of auroras is not with cer- 
tainty known, but they are thought to be an exchange be- 
tween the electricity of the atmosphere and that of the 
earth. The arch of the aurora nearly always surrounds 
the earth's magnetic pole. 11 

Magnetism. — A bar of steel, iron, or nickel, or a piece 
of lodestone n that has the property of attracting and 
holding to its surface small pieces of similar metals is 
called a magnet. Steel retains its magnetism permanently, 
and for all practical purposes the magnet is a flat bar of 
polished steel, eight or ten inches in length. Sometimes, 
however, it is bent into a U-shaped form called a horse- 
shoe magnet. 

When a bar of steel is magnetized, it is found that the 
magnetic force is not uniformly distributed throughout the 
bar, but is most intense at or near the ends. 1,3 These are 
the poles of the magnet ; they aro designated as positive 
+ , and negative — , according to the direction they take 
when the magnet is suspended at the centre of gravity. 

If a slender bar of ordinary steel be suspended by a hair 
from its centre of gravity, it will lie indifferently in any 
direction in which it is placed. If the bar be magnetized, 
however, it takes new properties. It no longer remains in- 
differently in any position ; on the contrary it turns until 
its direction is nearly or quite north and south. It no 
longer remains balanced, but the north-pointing end dips 
toward the earth. 

If now another bar magnet be brought near it, the latter 
shows no little sensitiveness. If the + end of the bar be 
presented to the + end of the suspended magnet, the latter 
will instantly turn away ; if the two — ends be brought to- 
gether the same thing will be noticed. On the contrary it 
+ and — poles bo brought together they are strongly at- 



274 



PHYSICAL GEOGRAPHY 



tracted. From these experiments the laws of magnetism 
are deduced. Like magnetic poles repel ; unlike poles at- 
tract. Either pole of the magnet, however, will attract 
alike an unmagnetized piece of iron or steel. 

It is upon these laws that the whole science of naviga- 
tion by the compass depends, for the earth behaves as a 
magnet 14 and the essential part of the mariner's compass is 
also a magnet. 

Magnetic Variation. — The earth's magnetic poles are 
not situated at the geographical poles. The magnetic north 
pole is situated west of Boothia Land, a few miles north 
of the crossing of the 97th meridian and the 70th parallel. 




LINES OF EQUAL MAGNETIC VARIATION 



Its position is not fixed, and it is moving in a westerly di- 
rection. 15 The position of the magnetic south pole is not 
known, although roughly approximated. 

Because the magnetic poles are not situated at the geo- 
graphic poles, it is evident that the magnetic needle can 



ELECTRICAL AND LUMINOUS PHENOMENA 275 

point due north and south in but few places. In the ac- 
companying chart, a heavy black line passes through 
these points. This line, called the agonic, is the line of 
no variation. West of this line the north-pointing end of 
the needle turns toward the east, and east of it it swerves 
to the west. Along each of the lighter lines the needle 
has the same deviation at all j^oints, and these lines, there- 
fore are called isogonics or lines of equal variation. This 
deviation from the true meridian is called declination. 

Trace the course of the line of no variation. 

Besides that element of magnetic force that causes the 
needle to lie in a nearly north-and-south direction, there 
is another that causes it to dip or incline one end toward 
the earth. This is called the vertical force, or inclination. 
Along an irregular line passing around the earth, some- 
. times north of the equator and sometimes south of it, 
the needle has an absolutely horizontal position. North 
of this line the negative, or north-pointing end, dips 
toward the earth. The farther the observer goes north- 
ward, the stronger becomes the vertical force, and when 
the magnetic north-pole is reached the needle has a ver- 
tical position, the — pole being next the earth. 

South of the magnetic equator, or aclinal, the conditions 
are reversed. The + pole dips more and more, until, at 
the magnetic south pole, the needle is again vertical with 
the + pole next the earth. A line on which the dip is 
everywhere the same is called an isoclinal. 

Not only does the position of each isogonic vary from 
time to time, but the rate of variation is not uniform ; even 
at the same place the rate varies from year to year. In 
the northwestern part of the United States the amount of 
variation is at present from 3' to T ; in the southwestern 
part it is, at present, nothing ; in the eastern and central 
parts it varies from 5' to 3'. 



276 PHYSICAL GEOGRAPHY 

The deviation from the true geographical meridian also 
varies from day to day. Most of these variations are 
periodical. Some are daily, some monthly, and some 
yearly ; they are probably caused by the daily rotation of 
the earth, the passage of the moon, and the annual motion 
of the earth. There are also irregular changes in variation 
which cannot be accounted for. 

Such changes in variation are rarely great ; in temperate 
and in low latitudes they cannot % well be detected except 
by close measurements. In the vicinity of the magnetic 
pole, however, they are more marked. At Point Barrow 
and at Lady Franklin Bay, during a period of twenty-four 
hours, a change of nearly eleven degrees was recorded. 10 

Magnetic Storms. — Not infrequently the irregular vari- 
ations of the needle are so violent that they have been 
called magnetic " storms," and during the progress of one 
of these disturbances the needle is in a constant tremor. 
Magnetic storms seem to be closely associated with the 
spots that at times are visible on the surface of the sun. 
The sudden formation or change in the position of a sun- 
spot is nearly always attended by great magnetic disturb- 
ances. The period when they are most frequent, more- 
over, corresponds to the period when sun spots are most 
numerous. 17 

The Mariner's Compass. — The compass is a slender 
bar of magnetized steel, so constructed as to balance on a 
pivot and turn freely upon it as well. Usually it is armed 
with a sliding weight, so adjusted that it exactly counter- 
balances the dip or vertical force, thereby keeping the 
needle in a horizontal position. 

On land the compass is of but little practical use except 
in rough surveys. On the sea, however, it furnishes the 
only means by which a vessel may be kept continually on 
her course. For this reason the mariner's compass is 



NLKCTRICAL AND LUMINOUS I'll KNOM UNA >;; 



constructed with the greatest care and precision. 18 The 

needle, which consists of one or more slender bars of steel, 
is fastened to a circular card subdivided into thirty-two 
parts, on which are printed the cardinal directions. These 
are called points of the compass. The compass-box is 
mounted on gimbals, so that, no matter what may be the 
motion of the vessel, the box always swings into a hori- 
zontal position. 

In going over almost every travelled ocean route, 
the variation of the compass changes day by day. On 
the regular routes of the 
transatlantic liners, the 
variation increases from 
about eight degrees at 
New York to more than 
thirty -five degrees at the 
crossing of the 40th me- 
ridian. It then decreases 
to about twenty degrees 
at Liverpool. 

In arctic regions, where 
the horizontal element of 
force is so weak, and the 
dipping force so strong, 
sailing by compass is a very difficult matter. Not only 
does the variation change rapidly over short courses, but 
the needle becomes exceeding sluggish. On whaling ves- 
sels it is customary to attach a line to the compass-box so 
that the steersman, by occasionally slinking it, may better 
judge the course over which the vessel is sailing. 

Luminous Phenomena. — Transparent as it seems, the 
atmosphere nevertheless does not afford passage to all the 
light that may bo transmitted through it. A ray of light 
in passing obliquely is not only refracted, or bent out of 




MAU1NHRS COMPASS 
An ordinary pattern. 



278 PHYSICAL GEOGRAPHY 

the direction in which it started, bnt possibly it is decom- 
posed into differently colored rays. The distortion that 
one may observe by looking at an object across the top of 
a very hot stove, or a smoke-burning chimney is an ex- 
ample of refraction. On the other hand, the color effects 
observed when light passes through a glass prism, such as 
a chandelier pendant, or even the bevelled edge of plate- 
glass, are examples of decomposition — the beautiful dis- 
play of the colors red, green, and violet, with their com- 
pounds resulting. 

A ray of light striking the surface of a highly polished 
metal or vitreous substance is reflected, rebounding in the 
same manner as does a rubber ball thrown against the floor. 
The same thing occurs when the ray strikes the surface of 
a body of water, or even that of two layers of air resting 
one upon the other. 

The air always contains innumerable dust-motes and 
particles of matter so fine and light that they seem always 
to float. This is seen when a few rays are admitted into a 
darkened room ; the passage of the rays is marked by the 
light reflected by the motes; and it follows, therefore, that 
a part of the light emanating from a luminous source is 
always scattered. The scattering of the light in this 
manner is called diffraction. It is a singular fact, more- 
over, that some kinds of floating matter will scatter the 
blue, while other kinds scatter the red rays. 

The color of the sky is thought to result from diffrac- 
tion. The red rays are scattered and the blue rays ordi- 
narily reach the eye. At times, however, when the air is 
heavy with dust, the sky acquires a hue that is distinctly 
red. This was very noticeable in 1883, after the eruption 
of Krakatoa ; for nearly a year the sunsets were exceed- 
ingly lurid. Ordinarily, at sea, the blueness of the sky is 
very marked, and the color is purer than on land ; with ac- 



ELECTRICAL AND LUMINOUS PHENOMENA 279 

cumulating moisture, however, it may acquire purplish 
tints. At very great elevations, also, the blue gives way 
to a dead hue that approaches blackness. 

Mirages. — When a layer of air rests on another of 
different temperature and density, the surface of contact 
often reflects so much light that it acts as a mirror. If the 
surface is lower than the eye of the observer, the reflection 
much resembles that produced by a body of water, and a 
mirage results. In deserts and arid regions, the illusion is 
so perfect that nothing but experience will enable one to 
distinguish the mirage from a lake. The " lake " mirages 
of the Colorado Desert have lured both cattle herds and 
travellers to their death. 

With the reflecting surface above the eye, the character 
of the mirage differs. Thus, at times, off the lake shore 
at Chicago, one may see the lighthouse and the shipping at 
the mouth of the river inverted in the air. If possible, 
illustrate this by means of a large mirror held overhead, 
face downward. 

Still another form of mirage occurs when objects, ordi- 
narily hidden by the earth's curvature, are brought in 
sight. It sometimes happens that the rays of light reflect- 
ed from an object, are refracted so that they are curved 
slightly toward the earth, and a distant object is thereby 
brought to view. This phenomenon occurs at times along 
the Mediterranean and Red Seas, and it is not unknown 
along the Great Lakes. As a rule, a dry, still atmosphere 
is essential to the formation of the mirage. 

Coronas and Halos. — The ring or rings about the sun 
or the moon are very common phenomena. The small 
rings are coronas ; the larger ones, halos. In the case of 
the corona, which is not of very common occurrence, there 
is usually a series of concentric, colored rings. These, it 
is thought, result from diffraction, the light being scattered 



280 



PHYSICAL GEOGRAPHY 



by the moisture of the atmosphere. The halo around the 
moon is probably caused by refraction, and it appears 
when the air is very moist. For this reason it is apt to 
portend rain or snow. 

The halos of the sun, which are associated usually with 
cold weather, probably are caused by the refraction of the 
light as the latter passes through the ice crystals of cirrus 




HALOS OBSERVED BY GENERAL GREELY 

clouds. Frequently there are several circles. Some of 
them are concentric ; some are tangent one to another ; 
and some intersect one another. At the places of inter- 
section and of tangency more light is radiated, and these 
spots, therefore, are sometimes very bright ; they form the 
sun dogs, or mock suns. 

Rainbows. — Occasionally, during a summer shower, 
when the sun breaks through a rift in the clouds, the light 
passes through the falling drops of water in such a way 
that it is not only refracted but decomposed. The resulting 



ELECTRICAL AND LUMINOUS PHENOMENA 281 

decomposition is the arch of colored light that constitutes 
the rainbow. The bow is blue and violet on the inner, and 
red on the outer side. Sometimes there is a larger second- 
ary box in which the order of colors is reversed. 

The rainbow is best observed when the sun is near the 
horizon. The observer sees the bow when his back is 
turned toward the sun. The rainboAv is frequently ob- 
servable when heavy waves break and send spray high 
into the air, and also in the ascending spray of cascades. 

QUESTIONS AND EXERCISES.— Verify the statements concern- 
ing the mutual attraction and repulsion of electrified bodies, observing 
the directions contained in note i. 

Verify the statements concerning the laws of magnetism noted on 
p. 273, using one or more stout knitting-needles and strands untwisted 
from silk thread. For observing inclination the strand of silk had 
better be fastened by means of a slip knot to the needle ; for the other 
experiments the needle may be thrust through a bit of paper to which 
the silk is attached. In magnetizing the needles, rub the ends only. 

From the chart, p. 274, estimate the magnetic variation of the place 
in which you live. 

At any time of their occurrence note carefully whatever you may ob- 
serve with reference to auroras, mock suns, halos, and coronas. 

Observe whether halos of the moon are followed by clear or by rainy 
weather. 

Occasionally, in very dry weather the disc of the sun is considerably 
distorted at the time of setting ; explain why. 

Explain the cause of redness that occasionally marks sunrise and sun- 
set when the air is smoky. 

The sun and the moon seem to be much larger when near the horizon 
than at zenith ; is this phenomenon real or apparent ? The use of a 
paper or other tube an inch or two in diameter will aid in the solution 
of this question. 

Explain the phenomenon of the " sun's drawing water." 

COLLATERAL READING AND REFERENCE. 

Waldo. — Elements of Meteorology — pp. lGG-lyo. 
<iUKKi;Y. — American Weather. 
Davis— Elements of Meteorology. 



282 PHYSICAL GEOGRAPHY 



NOTES. 

' Small pieces of cork will answer for these striking experi- 
ments, but bits of alder pith are better. In order that they may 
be successful the air of the room should be very dry. The pith- 
balls may hang from the end of a penholder thrust obliquely 
into the cork of a stoppered bottle. For the electrifiers, a glass 
lamp chimney and a vulcanite comb may be used. Each must 
be made absolutely clean, as the slight film of grease from the 
hands will interfere with the reaction. 

2 The potential of electricity may be also likened to pressure on 
water flowing through a pipe. If the pressure be low the water 
will flow quietly through the pipe and fall at no great distance 
from the end of the nozzle ; on the contrary, if the pressure be 
great, it will be projected to a considerable distance. In a single 
cell of galvanic battery the potential, about one or two volts, is 
so low that the electricity will not jump across a space of one 
thousandth of an inch ; the quantity, moreover, is very small. 
In an electric-light wire a current of considerable volume will 
leap across a space one-tenth of an inch or more ; its potential 
is about 1,000 to 1,500 times as great as that found in a cell of 
an ordinary galvanic battery, being from 2,000 to 5,000 volts. A 
good Motional electric machine will cause sparks to leap between 
points ten or twelve inches apart ; the potential is very high, but 
the quantity is small. During a thunder-storm a stroke of light- 
ning may jump a distance of a mile. Not only is the quantity 
enormous, but the potential is so great as to be immeasurable by 
ordinary standards. 

3 At different localities, the character of the electricity may be 
so very unlike, that the earth, currents are sufficient to operate 
telegraph wires without the aid of the batteries. In regions of 
dry climate such conditions are more frequent than in areas of 
considerable rainfall. 

4 The vapor of water is not only a good conductor of electricity, 
but it is an excellent storage reservoir as well. The small glob- 
ules of vapor that compose the cloud mass carry each the charge 
of electricity upon the surface. But when a great number of 
these globules are condensed to form a drop of water, the surface 
of the drop is infinitely smaller than the aggregate surface of the 



ELECTEICAL AND LUMINOUS PHENOMENA 283 

globules. The potential of the drop, in comparison with that of 
the globules, is enormously increased. If an electrified body, such 
as a vulcanite rule, is brought near a sprayer or a sprinkler the 
fine spray immediately gives place to large drops. 

6 The lightning itself, or rather the electricity, is not necessarily 
visible. The flash of light that accompanies the discharge is 
due to some extent to the foreign matter in the path of the dis- 
charge, heated to whiteness. The air being a poor conductor 
offers considerable resistance to the passage of the electricity, 
and is therefore intensely heated along the line of discharge. 
The thunder is produced in exactly the same manner as is the 
noise that accompanies the discharge of a firearm. The air at 
the point of discharge is rarefied almost to the extent of being a 
vacuum ; the rush of the air to fill the suddenly made vacuum 
is accompanied by noise. The rumbling of the thunder is due 
partly to echo and reverberation, and partly to the fact that the 
sound along the line of discharge reaches the ear at different in- 
tervals — the greater the distance the longer the time required for 
the sound to reach the ear. Discharges of high potential only are 
accompanied by thunder. 

6 In paintings and illustrations it has always been customary 
to depict the electric discharge in the form of a zigzag line of 
many sharp angles. In the past few years photographs of the 
lightning stroke have been successfully made. One of these on 
a preceding page shows the fallacy of former notions on the 
subject. 

7 This reflection is called heat lightning. It is rarely ever ob- 
served except at the horizon when the latter is overcast by clouds. 
The reflected flashes of light are usually so far away that the 
accompanying thunder is not heard. 

8 While Cfesar was engaged in carrying on his military opera- 
tions in Africa, he relates that, during a severe hail-storm, the 
spears of his fifth legion were tipped with fire. The phenomenon 
was undoubtedly identical with that of St. Elmo's fire. It is not 
improbable that the " ignis fatuus," " Jack o' lantern," or "Will 
o' the wisp" is a similar electric phenomenon. Tbis is a hazy 
indistinct light that appears occasionally in swamps. According 
to tradition and fiction, the ignis fatuus is a bright light that 
moves rapidly from place to place mainly for the purpose of allur- 
ing unsuspecting travellers into dangerous places. As a matter 



284 PHYSICAL GEOGRAPHY 

of fact, it has no great power of locomotion, and practically is 
stationary. 

9 The aurora is not confined to northern regions ; it occurs in 
southern circumpolar regions as well. In the southern hemi- 
sphere, however, it is called the aurora australis, but the south- 
ern aurora is neither so brilliant nor so frequent in occurrence 
as that of the northern regions. 

10 It must not be thought that the aurora occurs at night-time 
only ; it may take place at any time — day or night. It is not 
visible in day-time, however, on account of the greater brilliance 
of the sun. 

11 Professor Balfour Stewart has advanced the opinion that 
both auroras and earth currents are secondary currents due to 
small but rapid changes in the earth's magnetism. The body of 
the earth may be compared to the magnetic core of an induction 
coil, the lower strata being the insulating medium, while the 
upper strata, which are much better conductors, take the part of 
a secondary coil. 

12 Nearly all the elements are more or less sensitive to magnet- 
ism ; iron, cobalt, and nickel possess the force most strongly, 
however. Bismuth and copper seem to be repelled and take an 
east-and-west position, or a direction at right angles to that of 
an ordinary magnet. Such substances are said to be diamagnet- 
ic. A piece of soft iron retains its magnetism only while it is in 
contact with a magnet or near to it ; a piece of steel, on the con- 
trary, once magnetized retains the property permanently. A steel 
bar may be magnetized by rubbing its ends with those of another 
magnet, or by winding several hundred turns of insulated wire 
about it, through which a current of electricity is passing. 

13 If the bar be a long one, or if the quality of the steel is not 
uniform, there are usually several supplemental poles scattered 
about the surface. For the same reasons a light slender bar is 
better than a stout one. 

14 The shape of the earth is not such that its magnetic force can 
possess much intensity. Several magnetic poles are known to ex- 
ist, but only the two north poles of great intensity are usually 
charted. The pole of greatest intensity is the one commonly 
known as the magnetic north pole. Since its discovery by Ross, 
it has moved about forty miles westward. In 1879 it was ap- 
proximately located by Lieutenant Schwatka in the open space 



ELECTRICAL AND LUMINOUS PHENOMENA 285 

between Victoria and Franklin Straits. Its exact position has 
not been determined since 1831, and it is doubtful if its location 
at that date was so precise as might be inferred from the figures, 
which are expressed in minutes of arc. At that time there were 
no instruments sufficiently delicate for such precise determina- 
tion. In 1884 the position of this pole was again approximately 
determined to be in lat. 70° 30' N. ; long, 96° 40' W. The po- 
sition of the magnetic south pole has not been with certainty 
discovered. 

' b Observations made at Paris on the movement of the magnetic 
north pole cover a period of more than three hundred years. In 
1580, the declination at the city was 11° 30' East. It decreased 
until in 1683 it was nothing, after which time the variation be- 
came west. The westerly variation increased until, in 1814, it 
amounted to about 22° 30' W. Since that time it has dropped to 
about 22°, and, it is thought, is slowly decreasing. In 1790 the 
variation at Norfolk, Va., was nothing ; in 1893 it was about 3° 
16' W. In New York City the variation in 1686 was 9° W. ; in 
1790 it had decreased to 4° 15' W. ; after this time, however, it 
gradually increased until, in 1893, it was about 8° 25' W. 

16 In order better to study these variations, magnetic observa- 
tories have been established in various parts of the world. The 
essential part of such an observatory is a series of magnets each 
carrying a small mirror, mounted in such a manner that a spot 
of light is thrown on a sheet of photographic paper. The sheets 
of paper are fastened each to a cylinder revolved by clockwork, 
so that the spot of light traverses the whole length of the sheet 
in twenty-four hours, thus drawing a line upon it. If the mag- 
net were motionless the line would be straight, but if the mag- 
net turns even a small fraction of a minute, the spot is thrown 
out of position and the line becomes irregular. Usually three 
magnets are employed — one to measure variations in horizontal 
force ; one for variations in vertical force ; and one to measure 
the strength of the horizontal force. 

17 This period recurs every eleven years. In 1882 the formation 
of a sun spot was attended by a magnetic storm that was recorded 
at Point Barrow, Lady Franklin Hay, Los Angeles, Kew (London), 
Cape Horn, and Paris. Telegraph instruments were affected, and 
in some instances, long circuits were worked by ground currents. 
At the magnetic observatory tlien in Los Angeles, California, 



286 PHYSICAL GEOGRAPHY 

the tremor of the magnets was so great that for several hours one 
of the instruments failed to make a legible record. 

18 In the Ritchie compass, now generally used in the United 
States Navy, the compass-box is filled with alcohol in which the 
card and needle almost float. The object being to relieve the 
bearing of the weight of the card, and thus make the needle more 
sensitive. It is a most excellent compass and is vastly superior 
to the ordinary compass formerly used. The compass of Sir 
William Thomson (Lord Kelvin), consists of a battery of six or 
more very slender magnets held in a skeleton frame. The latter 
is so light that the friction on the bearing is imperceptible. This 
compass is used in the English Navy, and by most of the trans- 
atlantic liners. As an efficient instrument it has no superior. 
The use of steel in the construction of vessels has added materi- 
ally to the difficulties of sailing by compass. The hull of a steel 
or iron vessel has poles of intensity peculiar to itself, and these 
are apt to change in time, so that frequent tests of the compasses 
are necessary. There are various devices for obtaining the 
proper correction for the compass on steel vessels ; a very effec- 
tive method is to swing the vessel, stem and stern, along a 
geographic meridian and then compare the observed with the 
normal variation. On battle-ships either the addition or the 
removal of the armament, or the substitution of a steel for a 
wooden mast, is apt to make readjustment of the compasses 
necessary. 



CHAPTER XVI 
CLIMATE AND ITS FACTORS 

The conditions of a region with reference to its habita- 
bility constitute its climate, and these, in general, are the 
results of heat and moisture ; climate, therefore, includes 
all the modifications of environment due to heat and cold, 
rain and drought. It is modified by many conditions, of 
which the principal are latitude, altitude, position of high- 
lands, direction and prevalence of winds, and the inclina- 
tion of the earth's axis, together with its constant parallel- 
ism to itself. 1 

Latitude. — Latitude affects climate chiefly with refer- 
ence to temperature. The greater the distance from the 
equator, the lower will be its average temperature. The 
sun's rays are never vertical beyond the tropics, and in 
polar regions they fall so obliquely that they impart but 
very little heat to the surface which they strike. Illustrate 
this by means of the diagram on p. 294. 

In going from the equator to polar regions, therefore, 
one will pass through about every degree of warmth from 
perpetual summer to the coldest winter. Within thirty 
or thirty-five degrees of the equator the change in tempera- 
ture is not great, but beyond the forty-fifth parallel the 
winter climate grows rapidly cooler for every few degrees 
of increase. 

Latitude also exerts a considerable influence on rainfall. 
As a rule the rainfall is greatest within the torrid zone. 

287 



288 PHYSICAL GEOGRAPHY 

In the region of tropical calms, on the contrary, the rainfall 
is usually deficient. These calms are regions of descend- 
ing currents of the air, and the air being warmed by its 
descent, instead of chilled, but little rain falls. 

Altitude. — The effect of altitude is much the same as 
that of latitude. On an average the temperature is lower 
by about one degree for every three hundred feet of ascent. 
Thus, even in equatorial regions, one may rind on the 
slopes of snow-clad highlands all the intermediate degrees 
of temperature between perpetual summer and eternal 
winter. In Mexico the effects of altitude are finely illus- 
trated. The city and seaport, Vera Cruz, is intolerably 
hot and moist, yet less than two hundred miles away, the 
City of Mexico enjoys a climate that is dry, cool, and in- 
vigorating. The difference is due almost wholly to its alti- 
tude — about 7,000 feet above the sea-level. 

A still more striking example is found among the pla- 
teaus of the Colorado River. Hurricane Ledge is an 
almost vertical escarpment, 2,500 feet high, that forms 
the boundary between two plateaus. On the upper mesa 
the products are those of a temperate climate ; in the 
lower they are distinctly sub-tropical. It is scarcely more 
than a stone's throw from the former to the latter. 

Position of Mountains. — The existence of high moun- 
tain-ranges often determines the quantity of rain precip- 
itated upon the surface of a given region. In tropical lati- 
tudes rain-bearing winds blow from the east, and the eastern 
slopes of high ranges are therefore well watered, while 
the western slope is dry. In the temperate zones, on the 
other hand, the raiu winds are from the west; and the 
western slopes in consequence receive most of the rain, 
while the eastern side is comparatively dry. Thus, in the 
Peruvian Andes, the rain winds deluge the eastern slope, 
leaving the western side practically a desert. In the 



CLIMATE AND ITS FACTORS 289 

southern Andes, the conditions are reversed ; the rain 
falls on the western side while the eastern slope is arid. 

The effect of the absence of mountains is observable in 
Australia. Partly because of its latitude, but mainly for 
want of a high range, the greater part of the continent is 
a desert, and about the only rain that falls is precipitated 
on the highlands of the eastern side. In the great African 
desert, the few isolated ranges receive considerable rain 
on their summits, but none falls elsewhere. 

Distance from the Sea. — The proximity of the sea 
exerts a marked effect on climate, both with respect to tem- 
perature and moisture. The climate of a coast region is 
always more equable than that of a far inland or continental 
area. The reason therefor is apparent ; the air over the 
ocean has a much more uniform temperature than that 
over the land. The result is seen when the extremes of 
temperature are noted. For example, San Francisco and 
Leavenworth, Kan., have nearly the same mean temper- 
ature for the year. But while the difference between the 
summer and winter temperature of San Francisco is less 
than ten degrees (F.), that of Leavenworth is almost fifty 
degrees. 2 

Not all coast regions, however, enjoy a maritime climate. 
Because the winds of the temperate zones are, as a rule, 
westerly, in the eastern coast of such regions land winds 
are prevalent. The coast region of the northeastern part 
of the United States is an example. Its climate is dis- 
tinctively continental, and the influence of the sea pene- 
trates only a very few miles inland. 

The climate of islands at a distance from any large body 
of land is always equable. The Philippines and the Ha- 
waiian Islands are examples ; although in the torrid zone, 
they are regions of perpetual spring, with no excesses of 
temperature. The Leeward and Windward islands of the 



290 PHYSICAL GEO GRAPH Y 

West Indian group are also examples. Though situated 
only a few degrees north of the equator their summer tem- 
perature is less oppressive than that of New York City. 

Prevailing Winds. — Winds are the chief medium for 
the transmission both of moisture and warmth. Cold 
winds from polar regions modify the excessive heat of low 
latitudes, and tropical winds blowing into high latitudes 
soften the rigors of polar climate. The mild temperature 
of western Europe is due largely to southwesterly winds, 
and the same is true of the equable climate of western 
North America. Not only do the winds themselves trans- 
fer a great amount of heat by convection, but the vapor of 
water furnishes an enormous supply. For every pound of 
water vaporized, enough heat is made latent to raise nearly 
half a ton of water one degree (F.) in temperature. When 
the vapor, mingled with the wind, is carried to higher lati- 
tudes and there precipitated, all this heat is again set free. 
An inspection of the chart of winds (p. 221) readily gives 
all the information necessary to determine roughly the 
climate of a country. The regions invaded by sea winds 
that have come from low latitudes are the regions of warm 
and equable climate. Inland and polar regions are areas 
of climatic extremes. 

Changes in Climate. — As a rule, the climate of a 
country is constant ; that is, it does not change materially 
except after long intervals of time. The mean tempera- 
ture of any given locality rarely varies more than a very 
few degrees from one year to another, and the averages of 
long periods show still less variation. Fluctuations in rain- 
fall and cloudiness are considerably greater than those of 
temperature. In regions of generous rainfall the precipi- 
tation of very wet years may be nearly twice that of very 
dry years, but in localities of deficient rainfall the differ- 
ence may be greater. 



CLIMATE AND ITS FACTORS 291 

When time is reckoned by geological epochs, however, 
it seems certain that great climatic changes have occurred 
in every part of the earth, and that they have been of the 
most radical character. The Glacial Epoch, already de- 
scribed, is an example of a change in the climate that has 
taken place in the North Temperate Zone. It is certain 
that the rainfall of the Basin Region of the United States 
is subject to periods of oscillation. The few scattered 
sinks and salt lakes of the Great Basin itself are remnants 
of two large lakes that existed there at no very remote 
period, and these in turn are evidence of a much greater 
rainfall than the region receives at the present time. 

Definite knowledge of such changes, in the main, is cir- 
cumstantial, and statistics regarding them are almost 
wholly wanting. The cause or causes of such changes, 
moreover, are unknown. A change in the inclination of 
the earth's axis would be competent to account for changes 
in temperature, and therefore in rainfall. 1 Changes in in- 
clination have certainly occurred, but their definite effects 
are not known. Changes in the level of a region are also 
capable of producing variations in temperature, and it is 
highly probable that elevation and depression have re- 
sulted in many of the climatic changes of which there is 
an unwritten record. 4 

Zones of Climate. — Zones or belts whose limits are 
bounded by lines of equal average temperature are called 
isothermal or climatic zones, and the lines bounding them 
isothermal lines or isotherms. A comparison of the map of 
the astronomical and the climatic zones shows that the 
correspondence of the two is only general. The former 
are fixed and their boundary lines are parallels of latitude. 
The latter change their positions with the apparent motion 
of the sun, behaving in this respect like the zones of winds 
and calms. In fact they are all governed by the same law 




ISOTHERMS FOR JULY 




ISOTHERMS FOR JANUARY 



CLIMATE AND ITS FACTORS 293 

and arise from the same cause — the inclination and self- 
parallelism of the earth's axis. 

In the southern hemisphere the isotherms range ap- 
proximately with the parallels. What may be inferred 
from this concerning the uniformity of temperature with 
respect to latitude ? In the northern hemisphere the iso- 
therms are very irregular. In which direction do they 
bend in crossing the great highlands of the earth ? Explain 
the cause of this. In the North Atlantic warm ocean cur- 
rents and their drifts cause a deviation of the isotherms ; 
explain how and why. 

By what isotherms is the climatic torrid zone limited 
north and south ? 3 Compare the position in January and 
July. In the spring and the fall its position corresponds 
roughly with that of the astronomical zone. The hottest 
areas are situated not on the equator, however, but north 
of it. In the African desert, Arabia, and the arid lands of 
the United States, the summer temperature is above 38° 
(100° F.) and during unusual hot spells it sometimes 
reaches 49° (120° P.). 

The isothermal temperate zones are limited by the lines 
of 21° (70° F.) and 0° (32° F.). The summer limit of the 
northern zone extends high into the arctic regions. The 
winter limit on land approximates the fortieth parallel, but 
on the ocean it is much higher. In the Pacilic it reaches 
to the sixtieth parallel ; in the Atlantic, owing to the drift 
of the Gulf Stream it penetrates the polar latitudes. 

Extremes of Climate. — The isotherm of highest 
temperature that completely girdles the earth is theoreti- 
cally the thermal equator. Its temperature is probably 
between 27° and 30° (80° to 86° P.). There are several 
isolated regions having a considerably higher temperature, 
however. An extensive region in the Sahara has ;i mean 
temperature of about 29° (85° F.), and in Hindustan and 



294 



PHYSICAL GEOGKAPHY 



Africa there are others equally warm. In the American 
continent an oval-shaped region extending southward from 
the Gulf of California has about the same mean. 

The regions of extreme cold are not in the vicinity of 
the geographical pole, but considerably south of it. In the 
American continent the area of extreme cold is near the 
Arctic Archipelago. In Eurasia it is a little to the east- 
ward of the Lena River. In both regions the mean tem- 
perature is not higher than— 17° (0° F.). At Werchojansk, 6 
Siberia, the temperature ranges from — 67° (—90° F.) to 

32° (90° F.) a range 
of one hundred and 
eighty degrees — and 
probably the great- 
est on the earth. 

Changes of Sea- 
son. — Because the 
earth's axis is in- 
clined to the plane 
of its orbit, and re- 
mains parallel to it- 
self while the earth 
revolves around the 
sun, it follows that the rays of the sun do not fall on a 
given place always at the same angle. 

Exercise. — From the diagram above find the time at 
which the sun's rays are vertical at the tropic of Cancer. 
What is the season at this time in the northern hemisphere? 
Are the sun's rays direct or slanting in the southern hemi- 
sphere ? What is the season there ? What are the seasons 
when the sun's rays are vertical at the equator ? On a 
piece of thin paper trace, with a pencil, the isothermal hot 
zone on the map for January, p. 292 ; cut it out along the 
lines, and place it in its proper position (i.e., for January 




POSITION OF HEAT-RAYS IN'JUNE 



CLIMATE AND ITS FACTORS 



295 



on the map for July). The parts that overlap show the 
region where summer is continuous all the year. Compare 
this result with the diagram on this page. What parts are 
not covered by the 
heat -belt? When 
the heat-belt is far 
north what is the 
season in the North- 
ern Hemisphere ? 
in the Southern ? 
From the oscilla- 
tion of the heat- 
belt show how five 
zones of tempera'/ 
ture result. 

The inclination 
of the axis, together with its parallelism, as the earth re- 
volves around the sun, bring the temperate zones, in turn, 




POSITION OF HEAT-RAYS IN DECEMBER 




ANNUAL MOVEMENT OF THE HEAT-BELT 



to a position where the sun's ra} r s are nearly vertical. It 
is this movement that causes the shifting of the zoues 
of climate alternately north and south. 



296 PHYSICAL GEOGBAPHY 

The alternation of the four seasons is realized mainly in 
the temperate zones. In the greater part of the western 
coast of North America the seasons are distinguished more 
by the distribution of rain than by variations in tempera- 
ture. Practically there are two seasons — a rainy and a 
dry. Within the greater part of the torrid zone these are 
also about the only distinctions of season. In the frigid 
zones the distinctions of summer and winter are also those 
of day and night, each of which is six months in duration. 

Deserts. — There are many extensive areas that have 
little or no rainfall. If the rainfall is so deficient that 
irrigation is necessary to produce crops the region is said 
to be arid ; if it is too dry for food crops, it is generally 
considered a desert region. In many instances there is no 
sharply drawn line between fertile and arid lands, or be- 
tween arid lands and deserts. For instance, all that part 
of the Mississippi basin east of the 97th meridian, or more 
strictly, the 2,000-foot contour — produces an abundance of 
food stuff. West of this contour, however, the climate be- 
comes much drier, and beyond the 100th meridian or 
2,500-foot contour, crops must depend mainly on irriga- 
tion. 

Farther west, turf grass is replaced by scanty bunch 
grass, and beyond the crest of the eastern ranges of the 
Kocky Mountains the character of the country in places 
approaches that of a typical desert. In the northern part 
of the Basin Region, the cooler climate and the high 
ridges wring a small amount of water from the clouds, but 
in the south almost all vegetation disappears and the region 
is absolutely a desert. The same gradation is observed 
in the great African desert. Both north and south of the 
equatorial rain-belt, precipitation decreases little by little ; 
fertile lands grade imperceptibly into arid belts, and the 
latter into deserts. 



CLIMATE AND ITS FACTORS 297 

In the South American deserts the line, on the contrary, 
is pretty sharply drawn, and the same is true of the North 
American desert and the Sahara, if they are approached 
from the western side. In each case a high mountain- 
range forms a barrier to the rain winds, sharply dividing 
a fertile area from a desert. 

Only a small part of the extensive desert areas is desti- 
tute of vegetation, and in such parts the finely pulverized 
rock waste, or " sand " 7 shifts hither and thither with the 
winds. It is in such regions that the fierce simoon and sim- 
ilar sand-storms prevail. The Colorado Desert, in south- 
eastern California, is an excellent example of the kind. 

The climate of desert regions is marked Iry peculiarities 
and extremes. The winds are hot sand-blasts and whirls ; 
the scanty rains come usually in the form of cloud-bursts ; 
the temperature is one of frightful extremes ; the relative 
humidity of the atmosphere rarely exceeds thirty per cent, 
of saturation. Notwithstanding all this, desert climate is 
wonderfully healthful. 

Any fertile spot in a desert is called an oasis, and the 
latter is fertile because it is more or less abundantly sup- 
plied with water. On account of the presence of water, 
the oasis commonly yields a goodly supply of food-stuffs. 
Various causes contribute to the formation of oases. The 
underlying strata may be impervious to water, thereby 
preventing the latter from sinking deep into the soil, 
or there may be a mountain-crest that is sufficiently high 
to condense and precipitate more or less moisture. The 
water flowing down the slopes percolates through the fine 
rock waste at the bottom, much of it being held there in 
suspension. The oases of the North American deserts are 
of this character. 

The distribution of deserts constitutes an interesting 
study. There are practically two zones, situated mainly 



298 PHYSICAL GEOGRAPHY 

between the 20th and 50th parallels, north and south, that 
contain nearly all the desert and arid lands of the earth. In 
Eurasia and Africa a belt of desert stretches from the west- 
ern coast almost through the continent. 8 In North America 
this belt is nearly 1,000 miles east and west. The deserts 
of the Southern Hemisphere are smaller in area only be- 
cause of the smaller land area. In South America it lies 
at the eastern base of the Andes ; in Africa, south of the 
Kongo water-shed; in Australia, it extends almost across 
the continent. 

Various causes contribute to make arid and desert con- 
ditions ; but in any case a desert is a desert, not because 
of any natural sterility of the soil, but because of the lack 
of moisture. 9 In some localities a high mountain-range 
that faces the sea-winds condenses all the moisture they con- 
tain and the opposite slope with its outlying area is there- 
fore a desert. Explain why the Peruvian desert of South 
America is west of the Andes, and the desert of Argentina 
lies to the east of these ranges. Why is the region east 
of the Cascade and Sierra Nevada Ranges either arid or 
desert? What effects have the Himalaya Mountains on 
the rainfall of the region to the northward ? 

In other instances the desert conditions arise from other 
and more complex causes. Thus, between the 20th and 
30th parallels there is a downward movement of atmos- 
pheric currents ; explain why these may produce deficiency 
or absence of rainfall (p. 288). In some localities the 
winds blowing inland from the sea may enter localities 
having a temperature higher than that of the winds them- 
selves, and in such instances their moisture is not con- 
densed. The Australian and African deserts result mainly 
from one or the other, or both, of these causes. They are 
unfortunately situated with reference to latitude, and they 
also are lacking in high mountain-ranges. 



CLIMATE AND ITS FACTOES 299 

QUESTIONS AND EXERCISES.— Referring to any good map, de- 
termine the climate of South America from the following suggestions, 
giving a reason for each statement : What are the conditions of tem- 
perature of the northern part ? How do those of the southern part 
differ ? In which part is temperature the basis of the seasons ? In 
which is rainfall ? From which direction do the rains of the northern 
part come ? of the southern part ? What is the effect of the Andes 
Mountains on the distribution of the rainfall ? Give the location of 
the desert and arid regions. Note the effects of altitude on the climate 
of the highlands ; of the lowlands. What evidence does the map give 
to show whether the rainfall of the Amazon basin is profuse or deficient ? 
Explain why the basin of the Orinoco has two rainy and two dry 
seasons. 

Compare the Asian and American deserts as to origin. How do the 
African deserts compare in this respect ? 

Prepare a summary of the climatic conditions of the state or county 
in which you live, noting especially any facts not ordinarily included 
in the general outlines of the subject. From the United States Weather 
Bureau obtain the following : highest temperature observed, lowest 
temperature observed, mean for each month, mean annual rainfall, 
mean for each month, number of rainy days for any year, general 
direction of the winds, other relevant facts. 



COLLATERAL READING AND REFERENCE. 

Davis. — Elements of Meteorology. 
Waldo. — Elementary Meteorology. 
Greely. — American Weather. 



NOTES 

1 To these may be added the effect of ocean currents. It is 
sometimes stated that the warmth of western Europe — the Brit- 
ish Isles, especially — is due to the Gulf Stream, and that of the 
western United States to the influence of the Japan Current. 
So far as their temperature in general is concerned, such ;i state- 
ment is untenable. Ocean currents accomplish very potent re- 
sults, however, but not because of their effects on climate. 
Thus, the warm drift of the Gulf Stream is carried by the Pre- 
vailing Westerlies into about every bay and cove of western 



300 PHYSICAL GEOGRAPHY 

Europe; and as a result the harbors — even as far north as 
Hammerfest — are free from ice all the year. 

2 A noticeable and highly important difference between a mari- 
time and a continental climate, is the daily range of tempera- 
ture. In a maritime climate this rarely exceeds twenty degrees 
(F. ), while in a few inland regions the fluctuations may be twice 
as great. 

3 That is, if the axis of the earth were to incline forty degrees, 
then the polar and the tropical circles would have a correspond- 
ing distance from the poles and from the equator, and the tem- 
perate zones each would be ten degrees in width, instead of 
forty-three. Or, if the longitude of perihelion were to change 
materially, the winters of the northern hemisphere might be 
longer by several days than the summers, thus causing the ice 
and snow to collect faster than it would melt, thereby in time 
causing far-reaching changes. 

4 The elevation of a region is thought to result in a lowering of 
its mean temperature, and the depression of its surface, it is be- 
lieved, has an opposite effect. The surface of New York and the 
New England States was about 1,000 feet higher during the 
Glacial Epoch than at present. 

5 The mean annual temperature of a region reveals but little 
concerning its actual conditions of temperature. These can 
be studied only from monthly isotherms — that is, by comparing 
the monthly range of temperature and climate. For this reason, 
instead of a chart of annual isotherms, it has been deemed wiser 
to prepare two charts, one showing the isotherms for January, 
the other for July. 

Werchojansk or Verkoyansk is about four hundred miles north 
of Yakutsk, Siberia. The two are in probably the coldest inhab- 
ited region in the world. The highest temperature taken under 
standard conditions — that is, shaded by a double roof with an 
air-space between, and exposed at a distance from any radiating 
surface — seems to have been recorded at Warglar, Algeria, where 
the mercury marked 127° F. In the Colorado Desert an unoffi- 
cial temperature of 136° has been noted. In this case, however, 
it is doubtful if a properly exposed thermometer would have 
registered so much by ten or fifteen degrees. No temperature 
in this region recorded by the Weather Bureau has exceeded 122°, 
though there are several localities, such as Salton Lake and 



CLIMATE AND ITS FACTORS 301 

Death Valley, where the temperature ranges higher than at any 
of the Weather Bureau stations. The author has repeatedly 
noted temperatures in the Colorado Desert varying from 130° to 
145° registered by a thermometer exposed to the direct rays of the 
sun. The experience of General Gireely, U.S.A., Chief Signal 
Officer, shows the range of human endurance. At Fort Conger, 
Lady Franklin Bay, he and his party experienced no intolerable 
discomforts with the temperature as low as — 66°, the same officer 
served in Arizona where the shade temperature was 119° and that 
of an unprotected thermometer 144°. 

7 The shifting soil of deserts is popularly regarded as sand. As 
a matter of fact it consists of about every kind of rock waste 
broken and pulverized by the impact it receives as it is blown 
about by the wind. Doubtless it contains more or less quartz, 
but in general, true quartz sand is rare. In the Colorado and 
Mojave Deserts the detritus passing for sand is broken felspathic 
rock ; in certain localities of the Arabian Desert it is a red, loamy 
soil. 

8 ' ' The districts of the Sahara destitute of oases present a formid- 
able aspect. The path which tbe feet of the camels have marked 
out in the immense solitude points in a straight line toward the 
spot which the caravan wishes to reach. Sometimes these faint 
footmarks are covered with wind-blown rock waste, and the 
travellers are obliged to consult the compass, the horizon, a dis- 
tant sand-hill, a bush, a heap of camels' bones, or some other 
indications which the practised eye of the Tuareg alone can un- 
derstand as the means by which the road is recognized. Vege- 
tation is rare, and the only plants to be seen are the scrub, con- 
sisting mainly of thorny Mimosas ; in some sandy deserts there is 
a complete absence of all kinds of vegetation. The only animals 
to be found are scorpions, lizards, vipers, and ants. During the 
first few days of the journey a few indefatigable individuals of the 
fly tribe accompany the caravan, but they are soon killed by the 
heat; even the flea itself will not venture into these dreadful 
regions. The intense radiation of the enormous white or red 
surface of the desert dazzles the eyes ; in this blinding light 
every object appears to be clothed with a sombre and preter- 
natural tint. Occasionally the traveller, when sitting upon his 
camel, is seized with a kind of brain fever, which causes him to 
see the most fantastical objects in his delirium. Even those 



302 PHYSICAL GEOGRAPHY 

who retain the entire possession of their faculties and clearness 
of vision are beset by distant mirages ; palm-trees, groups of 
tents, shady mountains and sparkling cascades seem to dance 
before their eyes in misty vapor. When the wind blows hard, 
the traveller's body is beaten by grains of sand which penetrate 
even through his clothes and prick like needles. Stagnant pools 
or wells, dug with great labor in some hollow or other, from the 
sides of which oozes out a brackish moisture, point out each 
day the end of the stage. But often this unwholesome swamp, 
where they hoped to recruit their energies, is not to be found, 
and the people of the caravan must content themselves with the 
tainted water with which they filled thair flasks at the preceding 
stage. It is said that in times of great need travellers have been 
compelled to kill their dromedaries in order to quench their 
thirst in the nauseous liquid contained in the stomachs of these 
animals. ' ' — Elisee Reclus. 

9 In popular literature the climate of deserts is supposed to 
have baneful properties, and the expression " poisonous emana- 
tions ' ' has a prominent place in many newspaper accounts. As 
a matter of fact, desert air is unsurpassed so far as salubrity is 
concerned. It is so free from the germs that produce or hasten dis- 
ease, that meat will not putrefy and food will not ferment. Sep- 
ticaemia, or "blood-poisoning," rarely if ever follows accidental 
wounds or surgical operations, and tuberculosis originating in 
such localities is unknown. 



CHAPTEE XVII 
THE DISPEKSAL OF LIFE 

Theke are two lessons in nature that probably every 
human being of mature years has learned, namely — that 
the earth is full of organisms endowed with that mys- 
terious force called life, and that the life-forms are 
grouped in kinds or species. Moreover, while the indi- 
viduals of a species closely resemble one another, those 
of different species are commonly verj T unlike. 

Almost every living body or organism passes through 
several stages or conditions.' It first appears in the form 
of a germ enclosed in an envelope called an egg, or per- 
haps, a seed. Under the action of heat, or moisture, or 
both heat and moisture, the egg or seed passes through 
various stages of development in which it gradually ap- 
proaches its mature form — the condition that immediately 
precedes death. In general, the egg develops into a life- 
form, known as an animal, the seed into a plant. The egg 
may contain both food and moisture as well within its en- 
velope ; but the seed contains food only. The egg very 
easily loses its vitality or life principle ; the seed may re- 
tain its vitality for months, or even j'ears. The offspring 
of the egg almost always possesses the power of moving 
from place to place in one or another of its forms of life ; 
the offspring of the seed, on the contrary, cannot move ; 
it spends its life in the spot in which it developed into life. 

The seed-form of the organism is remarkably adapted 
for transportation and dispersal. Commonly the seeds 

303 



304 PHYSICAL GEOGRAPHY 

are strong enough to resist not a little mechanical force. 
Those of some species will endure a temperature but little 
lower than that of boiling water ; they will likewise endure 
the severest cold, and almost always they are enclosed in a 
water-tight case. The egg, on the other hand, will not 
endure extremes of temperature, nor will it survive the 
slightest injury. As a rule, both seeds and eggs float on 




A BARRIER THAT CERTAIN SPECIES CANNOT PASS 

water, and many kinds are so light that they are carried 
for miles in the air. 

The stage of growth and development is a condition of 
the greatest danger to the existence of the organism. 
During this period it quickly and easily succumbs to the 
most trifling changes in its surroundings. At this time, 
too, it is apt to be the prey of higher organisms that kill 



THE DISPERSAL OP LIFE 305 

and devour it. Indeed, so great is the mortality during 
the period of development that, in many species, not more 
than one or two individuals in many thousand reach the 
state of maturity. 2 

The mature stage of the organism follows that of de- 
velopment. In this condition it has but one objective 
toward which all its energies tend, namely — the reproduc- 
tion of its kind. This accomplished, sooner or later it dies ; 
that is, the vital principle leaves it, and it is quickly resolved 
into the mineral elements — the " dust " — which gave it ex- 
ternal form and structure. Not a few species have special 
means for the protection of their bodies, and nearly all 
possess special organs for the purpose of nutrition, and 
the higher species have organs of locomotion. 

Laws of Structure. — Many laws are concerned in the 
growth, development, and reproduction of organic forms, 
but there are three that govern, directly or indirectly, every 
form of life. These are heredity, nutrition, and variation. 

The law by virtue of which the germs of organisms de- 
velop and mature, each into a form of its own kind, is 
called heredity. The germ of a species always reproduces 
forms like those of the parents or ancestors. Acorns always 
produce oak-trees, animals beget each of its own kind, and 
the germ that in the human system produces disease, breeds 
nothing but disease of its own kind. ;5 

A seed or an egg develops into an organism that be- 
comes an ancestor of many thousand generations, aggre- 
gating millions of individuals. But in obedience to the 
law of heredity, the individuals of the last generation will 
not very greatly differ from their ancestor, nor will they 
differ from one another. 

The process by which food, once within the body of an 
organism, is decomposed and then made a part of the 
structure of the organism is called nutrition, or feeding. 



306 



PHYSICAL GEOGRAPHY 



In obedience to this law, new tissue, that is, flesh, blood, 
bones, etc., is constantly being made, and older tissue, no 
longer useful, is cast off and destroyed. The number of 
substances required in nutrition is few. Nearly three- 
quarters of the weight of every organic being consists of 
water ; in many instances 97 per cent, is 
water. The remaining part is composed 
mainly of compounds of carbon, nitrogen, 
hydrogen, and phosphorus. The food 
must contain all these substances or the 
organism will not mature. As a rule, 
plants obtain their food from the min- 
eral kingdom, and animals, either 
directly or indirectly, from plants. 
Variation is the law in obedi- 
ence to which organisms are 
changed, or change themselves, 
to meet the conditions 
necessary to their exist- 
ence. Thus, under cul- 
tivation, the wild rose, 
no longer needing its 
multitude of stamens, 
develops them into pet- 
als. Under the condi- 

VARIATION ADAPTED TO ITS ENVIRON- tioUS imposed b}' its 

MENT environment, the almond 

has varied its development by taking the form of the peach 
and the nectarine. 

Birds that for long-continued generations have obtained 
their food from the water have become either swimmers or 
waders, and many species of those that scratch the ground 
to obtain food have gradually lost the power of extended 
flight. The great diversity observable in the various mem- 




THE DISPERSAL OE LIFE 307 

bers of the dog family is a familiar example of the effects 
of variation. The horse of present times has but one toe, 
but the ancestors of the species in Miocene times had 
three, and in Eocene times four toes on the fore feet. 1 
The birds of early geological periods were much more rep- 
tilian in character than those of present times. Some of 
the reptiles, too, have lost their feet and are scarcely a 
remove from serpents. 

Environment. — Variation of species is the result of 
food, temperature, and moisture. These are the conditions 
with which every organism has to battle for existence, 
and these determine all its habits. If the environment of a 
species changes, one of three things is pretty certain to 
take place : the species dies, it migrates, or else it survives 
with changed habits. 

Thus, if in a given locality, the rainfall lessens materially, 
the turf grass quickly discovers it. In order to obtain the 
necessary moisture, an enormous development of rootlets 
takes place, and if this development does not procure the 
necessary amount of water, the turf grass gradually dis- 
appears. If a certain species requires an aggregate of ten 
inches of rain, distributed monthly, it will perish if the 
rainfall decreases to nine inches, or if there is a drought 
of more than thirty consecutive days. It will thrive and 
possibly extend its limits if the annual precipitation in- 
creases to twelve inches. 

The fruit of the common gooseberry, cultivated in moist 
regions, has a smooth surface ; but transplanted to arid 
regions and left to grow wild, the berry finally matures, 
covered with leathery spines. Cultivation, which is only 
another name for change of environment, has resulted in 
all the beautiful varieties of roses ; it has produced the 
domesticated fruits from wild fruits; it has made the dif- 
ference between the wild fowl and the domestic fowl of 



308 PHYSICAL GEOGRAPHY 

the same species. Since the territory inhabited by a 
species is either enlarged or decreased by a change in 
food, temperature, and moisture, and since a change in 
any of these factors sooner or later results in variation, it 
is evident that the distribution and variation of species is 
governed mainly by geographic laws. 

Causes that apparently are the most trivial are not in- 
frequently attended by far-reaching consequences. For 
example, the mongoose was introduced into Jamaica in 
order to exterminate the cane-rat, then a menace to the 
sugar-planter. The mongoose did not lessen the number 
of cane-rats, but it exterminated one or two species of 
ground-bird, and with their disappearance there came 
such swarms of " cattle-ticks " and " grass-lice " that the 
existence of cattle-raising was threatened. The ground - 
birds had prevented any great increase of the insect 
species ; but when the former were killed, the latter be- 
came an intolerable pest. 

Animals and Plants. — Plants are lower in the scale 
of life than animals. A few species excepted, they have 
not the power of voluntary motion, and if they possess 
the power of sensation at all, the latter is of the very 
feeblest degree. They derive their nutrition mainly from 
the ground and the air, being able to transform mineral 
matter, such as water, lime, potash, carbon, etc., into plant 
tissue. With one or two exceptions, plants inhale carbon 
dioxide and exhale oxygen. 

Plants exhibit only in the feeblest degree, if at all, the 
faculty of intelligence, and this is observed only in the 
way they seek their food. The roots of a plant will grow 
in the direction of water, and the flower will open with 
the light and close in the presence of darkness. No spe- 
cies is known that will pursue its prey or flee from an 
enemy. And the reason is obvious : the plant does not 



THE DISPERSAL OF LIFE 309 

exist at the expense of other life-forms ; it merely trans- 
forms dead mineral matter into living matter, which is to 
become the food of higher forms. Nevertheless, the plant 
contains a vital force that causes it to live, grow, develop, 
and reproduce; and when this vital force is spent, the 
plant dies. 

Animals — even the lowest species — are far more com- 
plex in organization than plants. The animal lives by the 
dest ruction of other forms of life, and therefore, in general, 
it must possess the powers of locomotion, prehension, or 
grasping, and also some means of defence. All animals 
possess intelligence, and some of the higher forms have the 
faculty of reason. No exact line of division, however, 
can be drawn between animals and plants. 
- Dispersal of Life. — The distribution of life over the 
globe is not a matter of chance ; on the contrary, it exhibits 
a character that can result only by the operation of fixed 
laws. Moreover it must be examined from two sides, 
namely — the means possessed by animals and plants 
to disperse and, conversely, the barriers that operate to 
prevent dispersal. 

The means of dispersal are many. All the higher species 
of animals possess the power of voluntary motion. Quad- 
rupeds use their feet; birds fly; nearly all insects have 
at least one stage of development in which they possess 
wings; and fishes swim. Marine currents cany many 
species from tin- place of their birth to distant parts ; and 
still other species arc carried by floating matter, and in 
the crop of birds. 

Seeds of plants are carried by the winds, by running 
waters, and in the crops of birds or in (lie digestive appa- 
ratus of animals. Commerce is responsible for the dis- 
persal of most species used for food and many that are 

baneful to humanity.'' In short, almost every organism 



310 PHYSICAL GEOGKAPHY 

possesses means that, under ordinary circumstances would 
give it a far wider territory than it now possesses. 

The natural or unrestricted migration of species presents 
an interesting aspect. In the temperate zones, as a rule, 
the dispersal has been from west to east ; in the torrid 
zone it has generally been in the opposite direction. A 
moment's thought will suffice to show the reason for this 
law, namely — the direction of atmospheric and marine 
currents. 

But there are many regions swept by marine currents in 
which the species they carry will not thrive, and quite as 
many traversed by winds that the winds never sow with 
seeds, and the soil never fertilizes. Such extraordinary 
effects cannot exist without causes, and these are the 
natural barriers to distribution. 

Barriers. — The barriers to dispersal are even more 
potent than its agents. These may be reduced to two 
classes — physiographic barriers and environment. Chief 
among the former are the high mountain-ranges, oceans 
and deserts. 

High mountain-ranges form a tolerably effective barrier 
to species not provided with means of locomotion, and the 
more extensive the highland the greater the difference of 
the species on the opposite sides. There are two reasons 
for this. In the first place, if the species are unprovided 
with means for migration they cannot cross it ; in the 
second place, the conditions of climate on the opposite 
sides of high mountains are so different that the species 
might not survive, even if transported. The low temper- 
ature of the summit of the range might also be fatal. 

The ocean and other wide expanses of water are effective 
barriers to land plants and animals. A few birds endowed 
with unusual powers of flight, have crossed the ocean ; 
seeds and eggs have also made the passage ; and not a few 



THE DISPERSAL OF LIEE 



311 



species have been transported in vessels. But all these 
are accidental migrations, and even then the question of 
environment would still remain to be determined. 

Deserts present the same difficulties. Few species are 
able to cross them ; fewer still to remain in them, and the 
barrier once surmounted, there may be changed conditions 
which still forbid the intrusion of the species. 

Environment has been considered in the light of a 
cause of variation, but it is far more potent as a barrier to 




A DbSBRT BARRltR 



the existence of a species. If a species requires a tempera- 
ture not lower than 0° (32° F.), it will perish in a climate 
having a lower range. If it requires an annual rainfall of 
thirty inches, it will perish if the precipitation falls to 
twent} T -nine inches; or if it requires a monthly distribution 
of rain, it will not survive any considerable number of 
droughts of more than thirty days. 



312 



PHYSICAL GEOGRAPHY 



Thus it is seen that every species demands certain con- 
ditions of food, temperature, and moisture. If these be of 
wide range the species will inhabit a wide geographical 
territory ; if they be narrow in range, the limits of its ex- 
istence will be correspondingly narrow. If the proportion, 
or degree, or quality change, even minutely, the species 
will vary ; if they vary materially the species will perish. 




THERE MAY BE ENEMIES THAT OPPOSE THE NEW-COMER 



It sometimes occurs, however, that a species, once in- 
troduced and acclimated, is unable to maintain itself, or 
maintaining itself, is unable to spread to any extent over 
a region whose soil and climate are in every way adapta- 
ble. There are several reasons for this. The region 
may have been already pre-empted by other species that 
resist encroachment, or there may be enemies constantly 
at work seeking to exterminate the new-comer. As a re- 



THE DISPERSAL OE LIFE 313 

suit, there are some species capable of general dispersion 
that are confined to narrow limits, while others have spread 
themselves broadcast over both continents. 

Thus, turf -grass is easily cultivated, but it has so many 
enemies that in a few localities only does it thrive in a 
wild state. The willow, on the contrary, spreads wherever 
it is introduced. The ostrich does not extend its territory, 
but the rabbit has become a pest in almost every part of 
the civilized world. 

QUESTIONS AND EXERCISES.— Study the common thistle, the 
dandelion, or the winged maple, and show how these species may be 
spread. 

In the temperate regions of North America in what general direction 
will those species depending on the winds for distribution be most 
apt to spread ? 

Note any instance that has come under your personal observation in 
which plants have been carried into new territory by winds, by running 
streams, or by waves. 

Note any instance within your knowledge in which either a natural 
feature or the activity of man has formed a barrier to the dispersion of a 
plant or an animal species. 

What advantages have each of the following species for dispersal ? 
the camel, man, the burdock, the ant, the snake, the cotton plant. 

The sting of the tsetse fly, an insect of Africa, is fatal to most cattle, 
but the offspring of those that survive, are immune from its attacks ; 
how will this fact affect the dispersal of cattle ? 

COLLATERAL READING AND REFERENCE 

Shaler. — Nature and Man in North America. 
Red way. — The Arid Region of the United States. 



NOTES 

1 Thus, among plants, these stages are the seed, the sprouting 
plant, and the mature, flowering stage. In aniinals they are the 
egg, the embryo, and the adult individual. Among the lower 
forms of life the changes are often far more complex. Most 



314 PHYSICAL GEOGRAPHY 

insects pass through the forms of egg, larva, pupa, and imago, 
and in some species there are still other intermediate forms. 

2 As the enemies to a species increase, its fecundity is apt also 
to increase. Thus, the spawn of a female cod-fish aggregates sev- 
eral million eggs. If all these were to hatch and mature, the sea 
would hold but a few generations. 

3 Since the discovery of the fact that many diseases are due to 
the growth and development of minute organisms within the 
human body, the science of surgery and that of sanitation have 
been greatly aided. Septicaemia, variously known as "hospital 
fever " and " blood-poisoning," once the bane of every hospital, 
are now comparatively rare, and such diseases as small-pox, 
typhoid fever, and cholera may be readily quarantined and 
stamped out. 

* Because of this struggle, that has been waging ever since life 
first appeared on the earth, only the individuals that can best 
adapt themselves to circumstances are able to survive. Varia- 
tion is not always a gradual change in a whole species ; it is 
quite as often a distinctive change in several individuals, and the 
transmitted change that marks the descendants. 

6 The Norwegian rat in America, the Colorado potato-beetle in 
Europe, and the English sparrow in the United States are exam- 
ples. The California species of the phylloxera, an aphis or 
plant-louse infesting the grape-vine, was introduced into France 
and almost destroyed the vines of that country. The Russian 
thistle at one time threatened to overrun the wheat-fields of the 
Mississippi basin, and the strictest means are necessary to keep 
it under control. The gypsy moth, whose larvse infests ripening 
fruit, has attacked the orchards of the New England States, and an 
expenditure of nearly a million dollars a year is necessary to keep 
its mischievous work in check. 



CHAPTER XVIII 



THE GEOGEAPHIC DISTRIBUTION OF PLANTS AND 
ANIMALS 

Not far from 150,000 species of plant 1 and nearly as 
niany of animal life are known to exist, and new species 
are discovered yearly. These are distributed in accordance 
with the laws noted in the previous chapter — that is, they 
live each in the locality best adapted to it. Plant life 
includes species that vary as widely in form and structure 
as the multitude of animal species. 

Distribution of Plants. — The distribution 2 of vegeta- 
tion may be considered in several aspects, namely — abun- 




FORESTRY OF THE NORTHERN REGION : OLD GROWTHS AND NEW 

315 



316 PHYSICAL GEOGRAPHY 

dance and kind ; and these are best studied with reference 
to their regional position or else according to their altitude. 
The abundance of vegetation is governed mainly by the 
conditions of temperature and moisture. In a climate that 
is both warm and moist there is nearly always an abun- 
dance of vegetation. Because of this fact, plant life is most 
abundant in tropical lowlands, decreasing as the latitude 
and the altitude increase. In tropical regions it is profuse ; 
in temperate climate, abundant ; in cold regions, scanty. 

With reference to the distribution of kind, two factors 
have been instrumental — environment and time. In the 
earlier geological ages certain species seem to have pre- 
vailed at certain centres, and from these they have spread 
in various directions. The area over which the species of 
a region may have spread is a question chiefly of time ; 
the locus, one of environment. The vegetation of a given 
region is called its flora. 

With respect to distribution the map on page 318 shows 
that five centres exist from which species have spread, or 
to which they are characteristic. 3 Name them. 

The Northern Regions, Eurasian and American, include 
the greater part of the two continents north of the Tropic 
of Cancer and that part of Africa north of the Atlas Moun- 
tains. The two regions contain, as natives, a large number 
of the deciduous trees, grains, and fruits. The grains, 
maize excepted, and most of the fruits are characteristic of 
the Eurasian; the redwood, sequoias, sugar-cane, tobacco, 
and the yuccas to the American region. The two regions 
are separated by the Atlantic Ocean, and though the life- 
forms are not identical they are very similar. 

The South American region embraces the territory south 
of the Tropic of Cancer, both mainland and insular. The 
mahogany, cinchona, india-rubber, and rosewood are among 
the chief species peculiar to the region. 



DISTRIBUTION OF PLANTS AND ANIMALS 317 

The African or Ethiopian region includes all of Africa 
south of the Atlas Mountains and tropical Arabia. The 
baobab, oil-palm, euphorbias, bigonias, the coffee-tree, 
several heaths, and the geranium, are among the native 
plants peculiar to this region. 

The Oriental Region includes the territory south of 
the Himalaya Mountains, and most of Malaysia. Among 
the principal characteristic species are the spices, the 
ebony, sandal-wood, and the melons. 

The Australian Region comprises the continent of Aus- 
tralia and most of the islands east and north. The flora 
of this area is highly peculiar. The prevailing color of the 
vegetation is bluish-green and the leaves turn their edges 
to the sun. The eucalyptus or gum trees, the various tree- 
.ferns, and the jarrah are peculiar to this region. In the 
north and east the Australian and Oriental regions over- 
lap, and are marked by species characteristic to both. The 
Eucalyptus and the tree-fern have been introduced into 
California; the jarrah is much used in the manufacture of 
street paving-blocks. 

The vertical distribution of species is determined by 
altitude Thus at the base of the Himalayas and the 
Andes, the flora is tropical ; higher up, the characteristic- 
species of the temperate zones replace tropical plants ; and 
at an altitude of twelve thousand feet, more or less, the 
vegetation is distinctly that of polar types. 

Economic Plants.— Most forms of plant life have an 
important relation to mankind, and this is especially true 
of those used as food, as medicine, or in the arts. Chief 
among them are the grains and other grasses, tuberous 
plants, fruits, those yielding textiles, and those used for 
building timber. 

The urnsses probably extend over a wider area than any 
other family. Of these the sugar-cane and maize, or Indian 



DISTRIBUTION OF PLANTS AND ANIMALS 319 

corn, are native to the American continent. All the others 
belong to the Old World, but have followed the march of 
mankind. The members of this family are the sole food 
of many hundred species of animals, and the seeds are 
consumed by every race and almost every tribe of man- 
kind. The starch they contain gives them their chief 
value as a food-stuff. 

Rice is confined chiefly to the marine marshes and 
swamp lands of tropical and sub-tropical regions, but there 
are one or more species of upland rice. Rice is the staple 
food of about one-half the people of the world. It is a 
notable fact, however, that in certain parts of China and 
India, wheat, little by little, is supplanting it. Pound for 
pound its nutrient value is not equal to that of wheat. 
Maize, or Indian corn, a native of the New World, is an im- 
portant food-stuff in temperate and sub-tropical regions. 
It is the chief bread-stuff of the " mixed "and native races 
of the New World. In the United States and Canada it 
is used mainly as animal food, being converted into pork. 
Its use, both in the form of grain and meat, is largely in- 
creasing among the peoples of the Old World. It is also 
used in the manufacture of liquor. 

Wheat is the bread- stuff of the civilized peoples of the 
temperate zones and, is the fuel of the activity and 
energy of the world. It is grown in the great plains of 
the temperate zones, but it thrives in sub-tropical and 
sub-polar regions. How do the topographic features, of a 
plain affect the harvesting and transportation of wheat? 
How do they affect the evolution of harvesting machinery? 

The world requires about 2,200,000,000 bushels of wheat 
each year, and the amount required is steadily increasing. 
Why? The annual crop is somewhat greater ; in 1898 it 
was 2,700,000,000 bushels. It is estimated that the maxi- 
mum crop possible is not far from twice this amount. 



320 PHYSICAL GEOGRAPHY 

About one-fourth of the world's crop is produced iu the 
United States. 

Rye takes the place of wheat in many countries, and is 
one of the most important crops of Russia and Germany. 
A species of oat is native to the North American region, 
but the cultivated plant is an imported variety. It is a fa- 
vorite food for horses. Barley, about the hardiest of 
the grains, is also much favored as a food for horses, but 
is employed mainly in the manufacture of malt liquors. 
Buckwheat 4 is not a wheat at all, but the nut or fruit con- 
tains a large percentage of starch ; hence it is much used 
as a food-stuff. 

The canes include one of the chief sugar-producing 
plants. 5 They thrive best in tropical countries, and are 
extensively cultivated in the sub-tropical belts. In oriental 
countries the bamboo, a species of cane, is much used as 
a building material and in the arts. 

The palms, next the grasses, probably yield the greatest 
variety of useful products. Cocoa-nuts, dates, sago, sugar, 
wine, and oil, are all derived from this family. So far as 
moisture is concerned, the palms have a wide range, but 
in respect to temperature they are restricted to warm 
regions. They occur in both hemispheres. 

Tuberous plants are among the important food-pro- 
ducers. The potato, probably a native of Chile, has been 
carried to every part of the civilized world. It thrives 
best in temperate latitudes. 

The yam 6 and its relative, the sweet potato, are indige- 
nous to tropical America. The beet and the turnip are 
native to Europe. The former is now the principal source 
of sugar. The cultivated onion seems to have come from 
China, but a wild variety occurs in America. The manioc 
(or manihot) is native to tropical America, but has been 
transplanted to Asia and Africa. 



DISTRIBUTION OF PLANTS AND ANIMALS 321 

The fruits are important, not only as delicacies, 7 but as 
foods. Among the foremost are the fig, the date, and the 
Corinth grape. They are native to the basin of the Medi- 
terranean Sea, and the dried fruit is a necessary article of 
food in that region. The banana, native to tropical Asia, 
has become a recognized article of food in America. 

The cultivated varieties of the apple, pear, peach, and 
plum are native to western Eurasia ; the cherry, apricot, 
and almond to the eastern part of that continent. The 
melons and their near relatives, the gourds (including the 
pumpkin and squash), are also from Asia. The orange, 
lemon, and lime probably came from the southern slope of 
the Himalaya Mountains. So far as written history is con- 
cerned, the grape 8 has a greater antiquity than any other 
fruit, manna possibly excepted. It is found in a wild 
state in both hemispheres. The cranberry probably orig- 
inated in the temperate zone of North America, migrating 
thence to Europe. The tomato is also native to America. 

Most of the succulent and leguminous plants, such as 
the cabbage, lettuce, spinach, and peas, have followed the 
migrations of Europeans. The bean seems to have come 
from Egypt. Celery is undoubtedly of Eurasian origin ; it 
is found in a wild state over a large part of the continent, 
but is extensively cultivated. 

The beverage-yielding plants in one or more species are 
cultivated throughout the whole civilized world. Tea is 
sent from eastern and southeastern Asia to almost every 
other country. The best quality is grown on the chain of 
islands east of the mainland ; it is also grown in the 
United States. Coffee is probably a native of Abyssinia, 
but is now cultivated mainly in the New World. It grows 
wild in the former region, and a similar species is native 
to the warm parts of California. 

The cacao-tree yields cocoa-beans. The latter, dried 



322 PHYSICAL GEOGRAPHY 

and browned, are used as an infusion ; ground with its 
own fat or with lard it is the chocolate of commerce. 
It is native to tropical America. Mate (ina-ta'), or Para- 
guay tea, is the leaf of a species of holly native to South 
America. Its infusion is used all over that grand divi- 
sion. 

The spices come nearly all from Southern Asia and the 
Malaysian archipelago. Of these none except pepper has 
been transplanted to any great distance from the place of 
their nativity. Capsicum, or red pepper {chile Colorado), 
is native to tropical America. Nutmeg is a fruit, the cov- 
ering of which is the mace of commerce ; cinnamon is the 
dried inner bark of a species of laurel ; cassia is a similar 
species growing in China and the New World ; cloves are 
the dried buds of a tree native to the Molucca Islands and 
Southern India. 

Medicinal plants are as widely dispersed as is the hu- 
man race. The opium -poppy, native to tropical Asia, pos- 
sibly to Egypt, has not migrated far from the place of its 
birth. The cinchona, a native of South America, but now 
cultivated in tropical Asia, yields quinine and a score of 
derivatives. The various members of the night-shade 
family 9 all yield powerful medicinal substances, among 
them nux vomica, strychnine, belladonna, and gelsemium ; 
they are found in both continents. 

Rhubarb and ginseng are native to China, but are now 
cultivated chiefly in the United States. The hemp that 
yields cannabis indica, or hasheesh, comes from south- 
ern Asia. Coca is native to the Andes. Cascara seems to 
be confined to tropical and sub-tropical America. Most 
medicines widely used are derived from plants found in 
tropical regions. Tobacco is native to America. 

Plants used in the arts have followed man in his migra- 
tions. Cotton 10 is the furze attached to the seeds of the 



DISTRIBUTION OF PLANTS AND ANIMALS 323 

cotton plant. Flax and hemp are obtained from the bark 
of flowering plants ; both came from the Old World — 
probably from Africa — bnt four-fifths of the world's prod- 
uct is now grown in the United States. Jute and ramie 
are native to Asia, but are now cultivated in America. 
More valuable than either of these is pita, the fibre of the 
wild pineapple, native to America ; and so also is hene- 
quen, or " sisal hemp," the fibre of the agave. 

The forestry of the world is distributed with a remarka- 
ble degree of regularity. The pines and other conifers, 
oaks, elms, maples, willows, chestnuts, and beeches, occupy 
a belt between the 40th and 55th parallels that crosses 
both continents. The distribution of tropical forestry is 
not so regular, from the fact that South America has a 
flora peculiar to itself. The palm, banana, mahogany, 
bamboo, and representatives of the pines continue through 
both continents, however. 

On both sides of the belts of forestry there are extensive 
treeless areas. In some instances the areas are treeless 
because they are deserts, but in others, such as the 
prairies and plains of Russia and the United States, there 
is a fertile soil and an adaptability of environment. In 
manv instances there are no trees because the seeds have 
not been carried thither ; because the rivers and the winds, 
flowing from regions that practically are deserts, carry no 
seeds into the regions toward which they flow. 

In the United States forestry thrives best in a gravelly 
soil, but lives and increases in a sedentary, prairie soil. 
In the Champlain period that followed the Glacial epoch, 
the northern part of the United States was traversed by 
streams that bore the seeds of various species. Wherever 
the streams deposited gravel they also deposited seeds. 
Hence this region was sooner or later covered with trees. 
As a matter of fact, the timber-covered regions of the 



324 



PHYSICAL GEOGRAPHY 



northern United States are nearly identical with the area 
covered by stream gravel and till. 

Distribution of Animals.— The animal life of a region 
constitutes its fauna. Of the various classes, 11 the mam- 
mals represent the highest types of life, both with respect 
to form and structure and also in the matter of intelligence. 
All the forms of animal life possess the attribute of in- 
stinct — the hereditary power of thought required in such 
actions as tend to preserve and extend life. The higher 




THE PENGUIN 
A type of Antarctic life 

forms, in addition, have the powers of reason. These 
faculties have, doubtless, largely controlled the distribu- 
tion of life. 

In the dispersal of animal species the power of locomo- 
tion has given a wonderful development to both instinct 
and reason, and these have been controlled by the most 
powerful motive that exists in connection with animate 
life, namely — the sense of hunger. 

As in the distribution of plants, there seem to be certain 
centres from which animal species have migrated. But the 
limits have been determined in a somewhat different way. 



326 PHYSICAL GEOGRAPHY 

In the case of plants the territory of a flora is mainly gov- 
erned by environment ; in the case of animal life environ- 
ment is an important matter, but the power of voluntary 
locomotion has been the leading factor. The limits of a 
fauna, therefore, are largely determined b} r its various 
physiographic barriers. 

In the map, page 318, it is seen that the North Amer- 
ican and Eurasian regions have a very broad extent, and 
are separated by marine barriers that are neither very 
wide nor impassable. In the south, the regions are sur- 
rounded by barriers that practically isolate them. For 
example, South America is separated from North America 
by the barriers of sea and climate. The African region has, 
in addition to these barriers, a high mountain range on its 
northern border ; the same is true of India, south of the 
Himalayas ; Australia is environed by the sea and also by 
peculiarities of climate. 

From this it may be inferred that the faunas of the two 
northern regions are not greatly dissimilar. Such an infer- 
ence is correct. In many instances the species are identi- 
cal, and in others an order or a class has its representatives 
in both continents. The southern regions, however, are 
marked by strong contrasts. 

The North American and Eurasian regions have in com- 
mon many species of carnivorous, or flesh-eating animals. 
Various species of wolf and bear are widely dispersed 
through both regions, and the cat family is represented by 
the panther and several species of wildcat. Many fur- 
bearing animals — notably the lynx, otter, ermine, badger, 
and sable — are common to both regions, and so are species 
of the deer family and mountain sheep. 

The grizzly bear, caribou,, bison, musk-ox and black 
bear are peculiar to America ; the first named is found 
only in the Rocky Mountain highlands. The reindeer, 



DISTRIBUTION OF PLANTS AND ANIMALS 327 

camel, 1 ' buffalo, and nearly all domestic animals are na- 
tive to the Old World, but have been transplanted to the 
American continent. The opossum, puma, bald eagle, 
humming-bird and wild turkey are native to the American 
region; the chamois, ibex, fallow-deer and aurochs are 
peculiar to the Old World. 

The South American Region is distinguished by a pro- 
fusion of animal life. The monkeys of this region are a 




13GRN OF THE SOUTH AMERICAN REGION: SURVIVES IN THE OLD WORLD 

species distinct from those of the Old World. The camel 13 
of the Old World is here replaced by the alpaca, vicuna, 
llama, and guanaco — all distantly related to the camel. 
The last named, however, is probably native to the South 
American region. 

The sloth, armadillo, ant-eater and peccary are peculiar 
to this region, and so are the numerous parroquets, and a 



328 PHYSICAL GEOGRAPHY 

host of insect life. The condor is the nearest approach 
to the European vulture and the rhea to the ostrich. 

The Ethiopian Region is conspicuous for the absence of 
the species most common elsewhere. On the other hand, 
the gorilla, lion, zebra, hippopotamus, giraffe, ostrich, live- 
toed elephant and many other characteristic species are 
found nowhere else. In but one other region is the pygmy, 
a dwarfed species of man, found. 14 

The Oriental Region is the birthplace of most of the 
domesticated animals. Among wild animals the tiger, 
mongoose, cobra, and three-toed elephant are peculiar to 
this region. The rhinoceros, jackal, and leopard are com- 
mon to this region and that to the westward. 

The Australian Region is marked by the most unusual 
types of life on the face of the earth. Almost all its life- 
forms are peculiar, and but few types found elsewhere 
occur in this continent. Many of the species are marsu- 
pials — that is, the female has a pouch or pocket in which 
the immature young are carried. Many others, such as 
the kangaroos, have enormously developed hinder legs. 
As a rule, Australian species are similar to those of a 
prior geological age. 

The Bearing of Organic Life upon Physiography. 
— In the foregoing paragraphs the effects of physiographic 
forces upon life have been considered. The bearing of 
life and its energy upon physiographic forms are just as 
far-reaching and quite as important. 

Life-forms have been and are now among the important 
agents in rock formation. Some of the limestone basins 
of the Mississippi Valley, all the infusorial earths, the 
various fringing reefs, the barrier reefs, the atolls, and the 
encircling reefs are the work of animal life. On even a 
more extended scale are the chalk formations of Western 
Europe, which are also the results of life. 



niSTWRUTION OF PLANTS AND ANIMALS 329 



In the broad areas of the tropical oceans the work of 
organic life is of still greater magnitude. The water of 
these regions is swarming with life, and the skeletons 
of the dead forms, together with other mineral constitu- 
ents, are accumulating at the bottom. Wherever deep-sea 




THE KANGAROO 
A type of the Australian region 

dredging has been carried on, these accumulations have 
been found. 

But the secretion of the lime from the sea-water lias had 
still another effect. After the lime and other mineral mat- 
ter has been absorbed by the organism, the water is speci- 
fically lighter, and, as a result, the change in the density 
of the water has brought about a slow, but a none the less 
certain circulation of water. 



330 PHYSICAL GEOGRAPHY 

Vegetable life also is responsible for extensive areas of 
rock formation. Under certain conditions, such as exces- 
sive saturation, the leaves, twigs, and stems of plants accu- 
mulate to considerable depths. If these accumulations be 
covered by overflowing sediment, either nuviatile or ma- 
rine, the wood-fibre, after long-continued pressure and par- 
tial decomposition, is converted into coal. 

In the United States more than 150,000 square miles of 
territory are underlain by coal measures, and in the various 
basins of Eurasia probably a greater area exists. The most 
extensive formations of this character are found in the later 
rocks of the Palaeozoic age, but coal is not confined to 
any particular strata. Coal-making has been an incident 
of every geological age. Diamond, graphite, anthracite, 
bituminous coal, mineral pitch, petroleum, and natural gas 
are all the results of organic life. 

In preventing general surface erosion, vegetation has 
also been an important factor. A surface covered with 
grass or foliage resists the action of rain and winds alike. 
Covered with vegetation a surface can withstand almost 
any amount of wind and rain, but denuded of vegetation, 
the surface is quickly scored by running water ; gullies 
grow into ravines, and the latter deepen into impassable 
canons. 

It has been shown in another chapter that not only 
is vegetation capable of converting a moderately dry region 
into a swamp, but also that it may fill the swamp and after- 
ward reconvert it into a dry region again. It may accom- 
plish even more than this. A single species, such as the 
Russian thistle, may exterminate every other species of 
plant within a certain area. 

As the native vegetation disappears so do the character- 
istic animals, and, sooner or later, the entire flora and 
fauna are changed. This changes also the character of 



DISTRIBUTION OF PLANTS AND ANIMALS 331 

the soil ; and as the topography of a region is due more or 
less to its characteristic vegetation, sooner or later this is 
changed. 

The very lowest forms of vegetable life, such as the 
moulds, the bacilli, bacteria, and micrococci, perform an 
important office also. These forms, commonly known as 
disease-germs, may — and sometimes do — exterminate whole 
species, both of animals and plants. In company with the 
mosses and lichens they disintegrate and decompose the 
hardest rocks and crumble them into soil. In w T arm, moist 
regions exposed rock-cliffs and strata are much rarer than 
in arid regions. Fresh surfaces of rock once exposed are 
quickly covered with mosses, lichens, and the various pro- 
tophytes. These, once established, require time only, 
either to completely disintegrate the rock, or else to cover 
its surface to a considerable depth. 

The common earthworm plays an important part also. 
It thrives in moist earth, and a colony of these worms, 
once bred in a given locality, continues to inhabit it until 
the whole mass is changed to a rich, loamy soil, capable 
of supporting a dense vegetation. Thus it is seen that the 
lowly and often invisible forms of life become important 
factors in the physiography of a region. 

QUESTIONS AND EXERCISES,— Make a list of the forest trees, 
shrubs, and other wild plants growing in the neighborhood in which 
you live. 

Make a special study of any plant or " weed " regarded as useless or 
baneful. If you cannot obtain the information you require, send a 
specimen to the Department of Agriculture, Washington, D. C. 

Follow the same directions with reference to the animal species, es- 
pecially those injurious to vegetation, applying to the Department of 
Agriculture for information you cannot obtain elsewhere. 

Enumerate the articles of food and table furniture used at dinner, and 
follow the route of each one from its native place to the table. 

Mention the various uses to which maize or the corn plant is put — 
grain, cob, and stalk. 



332 PHYSICAL GEOGRAPHY 

In what ways does the wheat crop affect the habitability of the 
United States ? 

Name some of the chief causes of the destruction of forestry. Note 
an instance in which the cultivation of the cotton plant has affected 
the history of a people. 

Describe instances in which the distribution of animals or of plants 
has been effected by the agency of mankind. 



COLLATERAL READING AND REFERENCE. 
Mill.— Realm of Nature, pp. 302-320. 

NOTES 

1 These are grouped in five sub-kingdoms. TJie protophytes are 
the lowest form of vegetable life. They consist each of a single 
cell or of groups of cells. In this sub-kingdom are included the 
yeast plant, and other similar substances known as ferments, the 
organisms that produce all the forms of ' ' rotting ' ' or putre- 
faction, and the host of bacilli, bacteria, and micrococci (com- 
monly known as ' ' microbes ' ' ) that are productive of disease and 
various structural changes. The TliallopTiytes include the plants 
in which there is little or no distinction between leaf and stem, 
such as lichens and fungi. Nearly all the ' ' sea- weeds ' ' and the 
vegetable ' ' moulds ' ' belong to this sub-kingdom. 

TJie bryophytes comprise the mosses and the liverworts. The 
pteridophytes rank a little higher. They include the club-mosses, 
horse-tail rushes, and true ferns. All the foregoing sub-kingdoms 
are flowerless ; they reproduce by means of minute spores that 
are borne in receptacles on some protected part of the plant. The 
dust coming from a bursting puff-ball consists of spores, and these 
have the reproductive properties of seeds or eggs. The phanero- 
gams include all the species of grasses, shrubs, flowering plants 
and forestry. Their growth, like that of certain lower forms, con- 
sists of two parts, the roots and the aerial portion. They repro- 
duce by means of flowers and seeds. 

2 This term is used here because, unfortunately, it is almost 
universally employed in the science of geography. What really 
has occurred to spread the species is a migration or a dispersal. 



DISTKIBUTION OF PLANTS AND ANIMALS 333 

3 This classification by regions or centres is practically the same 
as that proposed by Professor Wallace, except that the names 
E urasian, North American, and South American, are substitu- 
ted for palcearctic, nearctie, and neotropical. This scheme has 
been adopted because it is based strictly upon geographic laws. 

4 Buckwheat, for convenience, is included in this list. The 
name is a corruption of " beech- wheat, " on account of the resem- 
blance of the kernel to that of the beech-tree. It is said to have 
been introduced into Europe by the Saracens, and in parts of 
Europe it bears the name Saracen wheat. It probably came 
from Manchuria. 

5 To these should be added the beet, which is now extensively 
cultivated for the purpose of sugar-manufacture. In tropical 
America certain agaves, near relatives to the grasses, are the source 
of not a little sugar. 

6 The yam is found also in the East Indies, and it is a disputed 
question whether or not the American species is a descendant of 
that of India. 

7 This fruit is commonly but incorrectly known as a currant. 
The latter is regarded as native to Eurasia, but wild species are 
certainly indigenous to western North America. The apple and 
the plum, said to be native to Eurasia, are also found wild in 
North America. The peach seems to have originated in Persia, 
from which the name is derived. 

3 The fox grape, a wild fruit growing in Canada and the New 
England States, was discovered and described by the Norse ex- 
plorers who visited North America about A.D. 1000. The culti- 
vated species of America are mainly imported ; the Concord is an 
improved wild species of America. 

11 The potato, tomato, and tobacco are the most important Ameri- 
can representatives of this family. The " jimson " (probably a 
corruption of Janitstoini) and other species of the datura stramon- 
ium are found in all moist and warm regions of North America. 

10 Barbados and Sea-Island cotton is probably native to America. 

" The classification of animals is somewhat more difficult than 
that of plants. The animal kingdom is divided into eight greal 
branches or groups : these arc again divided info classes and sub- 
divided into the following orders : 

Protozoans, fbe lowest forms of animal lite, such as rhizopods, 
infusoria. Porifera, of which the sponges are the chief species. 



334 PHYSICAL GEOGRAPHY 

Ccelenterates, of which the coral -polyps, jelly-fish, and sea- 
anemones are the best types. Echinoderms, represented by the 
star-fishes, sea-urchins. Vermes, or true worms. Mollusks, or 
shell-fish, such as the oysters, clams, limpets, snails, and slugs. 
Arthropods, including the types of lobsters, crabs, spiders, scor- 
pions. Vertebrates, or animals having the back-bone. 

Of these the first four inhabit the water ; the remainder include 
both land and water animals. The vertebrates comprise various 
classes of which the principal are mammals, or warm-blooded 
animals that suckle their young ; birds, mainly aerial in their 
habits ; reptiles, including snakes, lizards, and turtles ; batra- 
chians, represented by frogs and toads, and fishes — all aquatic in 
their habits. 

r2 The factors that have governed the dispersal of animal 
species cannot always be determined. It must be borne in mind 
that dispersal began in prior geological times, when the condi- 
tions of environment were often different from those of the pres- 
ent age. In the case of marine life, the limits to the territory of 
species are bounded mainly by the temperature of the water. 
The fauna of cold currents is materially different from that of 
warm waters. Deep sea species are wholly different from surface 
species also. The fish living at the bottom of the deeper parts of 
the sea are mainly sharks, several new species of which were dis- 
covered by the Prince of Monaco at a depth of two miles. 

13 The camel probably originated in America, but became ex- 
tinct before the Glacial Epoch. In 1858 it was introduced into 
the Basin Region of the United States and a few head still sur- 
vive in the Gila Desert of Arizona. The popular distinction 
between the camel and the dromedary is a very misleading and 
an incorrect one. The term (derived from a Greek word, to run) 
first applied to a species remarkable for fleetness, afterward came 
to include any camel trained to fleetness of movement. 

11 There is some evidence of the existence of pygmies in Europe 
during the neolithic period, and recent discoveries in Switzer- 
land strongly confirm the evidence. Dr. E. M. Aaron has called 
attention to the fact that the archaeological l'ecords of Cozumel, 
an island east of Yucatan, bear evidence of the existence of a 
pygmy race. The ruins of the diminutive store-houses that are 
still found on the island, and the small human skulls lend credi- 
bility to the theory of pygmy existence in America. 



CHAPTER XIX 

MAN 

Man, though at the head of animate creation so far as 
the development of reasoning powers are concerned, from 
a physiological stand-point is distinctly an animal, and is 
closely related to other vertebrates. 1 The skeleton of a 
man does not differ materially in structure from that of 
a monkey, a bear, a dog, or a bat ; it does not differ very 
greatly from that of a whale, a lizard, or a bird ; it closely 
resembles that of the gorilla. 

With respect to nutrition the resemblance is still 
stronger. The digestive apparatus and the various 
processes by which food is converted into blood, bone, 
and flesh are the same in man as in other mammals. 
The food, moreover, is practically the same — water, grain, 
fruit, and the flesh of other animals. The organs by 
which the blood is circulated are the same, and the proc- 
esses involved in breathing do not differ in any essential 
point in man and other mammals. In the structure of 
bone, muscle, and tendon, 3 and in the operation of special 
organs, such as nerves, intestines, lungs, and heart, the 
functions are practically identical. 

The chief characteristic of mankind is the great develop- 
ment of the reasoning faculties. The power of reason is 
certainly common to some of the lower animals — possibly 
to all species. In man, however, this faculty is enormously 
developed in comparison with other animals. Moreover, 
the power of reasoning abstractly seems to be possessed 
by no other species of life. 

335 



336 PHYSICAL GEOGRAPHY 

The classification of mankind into races and families, 
however, is one of such great difficulty that no two eth- 
nographers are in full agreement. 3 Color of skin, texture 
of hair, and language have been each made the basis of 
classification, but each system, when closely followed, leads 
to confusing difficulties. 

The Black Peoples. — The people of this type are 
characterized by black skin, kinky or woolly hair, and thick 

lips. The Negroes are 
the best known people of 
the type. This race is 
native to Central Africa, 
but has been acclimated 
in America, numbering 
there about ten or twelve 
millions. The Bantus are 
the finest specimens of 
the black type, and in 
their native region are 

THE BLACK TYPE: A SAVAGE approaching civilization. 

They are distinguished 
by a color of skin that in some cases is distinctly bronze 
rather than black. Their features are finer, and the lips 
thinner than those of the Negro. 

The Australasians inhabit the continent of Australia and 
the near islands. They are tall and slender, have straight 
hair, and represent the lowest degree of civilization. The 
Melanesians are native to New Guinea and the chain of 
islands to the southeast. There are also tribes in various 
parts of the Philippine Islands. The Melanesians and 
Australasians are also called " Negroids." They are sav- 
ages, warlike and ferocious. Cannibalism is almost uni- 
versally practised among them, but is not confined to the 
black races. 




MAN 



337 



The black type of mankind is best adapted to a warm 
climate, and the various races are free from the malarial 
fevers and other baneful climatic influences that are so 
fatal to white peoples. In tropical regions the Negro races 
are by far the most enduring peoples. The religion of al- 
most all the people of this type is fetich or obeah worship. 

The Yellow Peoples. — The yellow or Turanic peoples 
are probably native to Asia somewhere north of the 
Himalaya Mountains. The type is characterized by 
coarse and straight black hair, high cheek-bones, and 






AMERICAN INDIANS 



yellow or yellowish -brown skins. In some instances, as 
the Chinese, the eyes are set at a peculiar angle, giving 
rise to the term " almond-eyed." 

The Chinese peoples 4 include the Chinese, Burmese, 
Anamese, and Siamese. Their civilization is an old one 
and highly elaborated. In religion the Chinese are nomi- 
nally Buddhists, but in fact they are given chiefly to an- 
cestor-worship. The Tibetans represent the best exam- 
ples of the race. The Burmese, Anamese, and Siamese 
are pure Buddhists. The Mongols of western and northern 
Asia, especially the high plateaus, are a race of nomadic 



338 PHYSICAL GEOGRAPHY 

horsemen, courageous and intelligent, but only a remove 
from the savage state. In religion they are Mohamme- 
dans. The offshoots of this race that have settled in 
Europe — the Turks, Huns, Laps, and Finns — have reached 
a high degree of civilization. 

The Japanese are probably a mixed race — Mongol and 
Malay, with which possibly there has been absorbed a still 
older race, native to the islands. Intellectually the Japa- 
nese are at the head of the race which they represent, and 
within forty years they have developed a civilization com- 
paring favorably with that of European nations. 

The Malays, or brown race, inhabit southeastern Asia, 
and the islands to the eastward. In their present state 
most of them are savage, but they seem to have the capa- 
bilities of an advanced civilization — a fact apparent in the 
Japanese, Javanese, and Hawaiians. The Maoris of New 
Zealand are an excellent type of Malay. The Hovas 5 of 
Madagascar, belong to this race. Most of the native peo- 
ples of the Philippine Islands are Malays. The Tagals 
have reached a condition of civilization ; the Visayas and 
Maccabeles are but little inferior ; the Moros are savages. 

The American " Indians," for the greater part charac- 
terized by a brown color, 6 are native to the American 
continent. At the time of the discovery of America several 
tribes, such as the Aztecs and Peruvians, were emerging 
from a state of barbarism into one of civilization. 7 They 
were gradually absorbed by their conquerors. 

In South America and Mexico the Indians have become 
a mixed race. For the greater part, this has resulted from 
inter-marriage with the Latin races — especially the Portu- 
guese and Spanish. In North America, on the contrary, 
where the associations between Indians and Teutonic 
peoples have always been marked by bitter hatred, the 
Indian blood is still pure, 



340 



PHYSICAL GEOGRAPHY 



The Eskimos, one of the most interesting divisions of 
the yellow type, are confined to the north circumpolar 
regions. They seem to be related to some one or other of 
the Mongol races, but the relation is distant. They are 
short in stature, averaging less than five feet in height. 
They are intelligent and highly susceptible to civilization. 
This fact is unusual, inasmuch as their habitations are mud 
and stone huts ; their occupation, fishing ; and their food, 

raw blubber and fish. 

The White Peo- 
ples. — This race com- 
prises two great divis- 
ions, each subdivided 
into various families. 
These divisions, more- 
over, represent lan- 
guage and relation, 
rather than structure. 
The color of the skin 
L varies from light 
blonde to swarthy, 
closely approximating 
black among certain 
peoples. Intellectual- 
ly, it is the dominat- 
ing type of mankind. 
The Aryan division is by far the most widely spread 
and numerous of the type. In Asia, it includes the 
Hindus, the Persians and most other dwellers in the Iran 
plateau. In Europe, it includes almost the entire popula- 
tion, the Turks, Huns, Lapps, Finns and Semitic peoples 
excepted. In the American continent, to Avhich its peoples 
have migrated, it embraces about one hundred millions of 
souls, mainly of the Teutonic family. 




WHITE TYPE: LATIN 



MAN 



341 



The Teutonic, Latin, Sclavonic, and Keltic families of 
this race now constitute the leading, most intellectual, and 
most powerful nations in the world. These families occupy 
most of Europe and the greater part of North America. 
Here the peoples of the various families are confusedly 
mixed by intermarriage. In South America they have 
intermarried with the 
native races. 

The Semitic family 
comprises the Hebrews, 
Moors, Arabs, and Abys- 
sinians. 8 The Assyri- 
ans and the Phoenicians 
were also of this race, 
but they have been ab- 
sorbed, or dispersed by 
conquest. The Hebrews 
or Jews are the only 
surviving remnant of 
this race now holding a 
position of any im- 
portance. For about 
four thousand years, 
in spite of fearful odds 
against them, they have held a commanding position. 

Springing from a family whose native place was not far 
from Syria, the Jews became a nation of considerable im- 
portance. Because of their steadfastness to their religion, 
neither slavery nor conquest has exterminated them. Scat- 
tered over the earth, they are numerically about as strong 
as ever they were, and their religion and ceremonial rites 
are as marked to-day as they were four thousand years ago. 

Pygmies. — Scattered over a considerable area of Africa 
are peoples having no ethnographic connection or relation 




WHITE TYPE : A REPRESENTATIVE OF 
THE HIGHEST CIVILIZATION 



342 



PHYSICAL GEOGEAPHY 



to any of the foregoing families. These are the pygmies. 9 
So far as the color of the skin is concerned, there are two 
classes of this people— one having a light brown skin, the 
other being almost black. 

Of the various pygmy tribes the best known are the 
Akka, Wambutti, and Batua of central Africa, and the 
Bushmen of the southern part. All individuals are charac- 
terized by a heavy growth 
of rusty, red-brown hair 
upon the bodies, prog- 
nathic jaws and retreat- 
ing foreheads. The aver- 
age stature of the Bush- 
men is about five feet ; 
of the other tribes about 
four and one-half feet. 
The Akka are character- 
ized by mis-shapen bod- 
ies, long, skinny fingers, 
and withered legs. The 
Negroids of the Philip- 
pine Islands are some- 
times classed anions: the 



pygmies. 

Nearly all the pygmy 

tribes have learned the 
use of fire, but, as a rule, they eat their food raw. Although 
they have a very low place in the human scale, they display 
considerable intelligence. The Wambutti are ingenious 
in devising nets and traps for securing game, and they 
seem capable of a low form of civilization. The pygmies 
are rarely at war either with the other African tribes or 
with one another. 

Antiquity of Man. — The written history of man does 




MAN 



343 



not extend backward more than six thousand years before 
the Christian era, and of this period the first half, as re- 
corded in Holy Scripture, contains data concerning but one 
or two families and their 
descendants. Geologi- 
cal history goes back to 
a period of greater an- 
tiquity, but unfortunate- 
ly gives no clew where- 
by the age. of man can 
be computed in years. 
Written history did not 
begin until man had 
reached a comparatively 
high state of civiliza- 
tion, but geological his- 
tory antedates this pe- 
riod, and discovers man 
living practically in a 
wild state, as a hunter 
and a dweller in caves. 

If man preceded the 
Glacial epoch, about 
every trace of the spe- 
cies disappeared. With 
a few exceptions, upon 
which doubt has been 
thrown, the oldest traces 
of mankind are found 
just above the unsorted 
drift of the Glacial 

epoch, and below that of the river gravels of Champlain 
times. Above the glacial drift, however, there can be no 
doubt of the existence of the species. 111 




YEI.I.OW TYPE : JAPANESE. 



344 



PHYSICAL GEOGRAPHY 



Both in Europe and America the bones of man, associ- 
ated with those of the cave-dwelling animals he hunted, 
have been abundantly found. With these have been found 
also implements of the chase, ornaments, charred pieces of 
bone, and in one instance a rude drawing of an extinct 
species of elephant, scratched on ivory. 11 

From the time of the earliest geological history of the 
species, there is observable one feature that distinguishes 




EMERGING FROM A SAVAGE STATE 



mankind from brute creation, namely — rapid intellectual 
development. Primitive man had learned the use of fire, 
and this in itself was to give him supremacy over all other 
animate nature. He had also acquired the use of tools, and 
these were a great increase of power. The earliest race of 
people employed hammers or axes of rough stone. The 



MAN 345 

next step seems to have been the making of polished stone 
axes, knives, arrow-heads, etc. When, however, the primi- 
tive man applied fire to the shaping of his tools and imple- 
ments made of metal, his civilization was assured, and his 
power became supreme. 

At first the metal employed was a crude alloy now known 
as bronze. At a later period, however, iron was substitu- 
ted for the alloy. Some of these implements were of an 
ornamental character, but in the main they were either 
tools or weapons. With the increased power afforded by 
these tools the people who used them pass out of the state 
of savagery and emerge into that of civilization. 

Migrations of Mankind. — The history of mankind is 
the history of successive migrations that have been going 
on for more than four thousand years. From the earliest 
times people have associated in families, families have 
grown into clans, and clans into tribes. When a region 
has been sparsely settled, association and government have 
commonly been of the patriarchal kind, the oldest one of 
the family or clan being the leader. 

In cases, however, where there has been a common 
enemy, the plan of association has often been communal 
as well as tribal. Thus while the families described in the 
earlier history of the Old Testament observed a patriarchal 
rule, in later times, the plan of government became com- 
munal and afterward national. The same evolution had 
began in the case of the aboriginal Americans. Families 
had grown into clans and tribes, and among the Aztecs and 
Peruvians, tribal association had grown into communal 
government and was fast emerging into civilization. 

But there have always been limits to the growth of a 
people. They may be exterminated by a stronger race ; 
they may be dispossessed by a stronger people or be ab- 
sorbed by them ; or they may find the region too much 



346 



PHYSICAL GEOGRAPHY 



overstocked, and incapable of supporting so great a popu- 
lation. In any case, unless the people is exterminated or 
absorbed, migration is the only remedy. 

Thus, tribes of the Tartar u race, known in history as 
the Huns, migrated from the plateaus of Asia and over- 
ran a large part of Europe. On their way they drove the 




THE HABITATIONS OF A BARBAROUS PEOPLE 



eastern Goths from their lands, and the latter, in turn, over- 
whelmed Italy and Spain. The Lombards, a Teutonic 
people, migrated from the shores of the Baltic to the Adri- 
atic Sea. The Vandals swept over western Europe, leaving 
behind a trail of fire and blood. They devastated Spain, 
crossed to Africa, and established an empire on the site of 
Carthage. About one hundred years later they were exter- 
minated by a Roman army. Under the teachings of Islam, 



MAN 347 

the Arabs (or Saracens) devastated the north of Africa, 
entered Spain and penetrated France. They founded a 
Moorish empire, but were afterward driven from Europe. 

The foregoing are but a few of the movements of popu- 
lation that occurred in the short space of three centuries, 
and in the smallest natural division of land. History takes 
no note of similar changes that must have been going on in 
other parts of the world at the same time. 

The records of unwritten history furnish many instances 
of the dispersions of peoples that must have taken place 
on a considerably greater scale. In some instances the 
migration was a systematic movement that practically was 
the advance of an army ; in other instances it was a grad- 
ual extension of limits. 

The migration of the Aryan race is an illustration of 
systematic dispersion. From some part of Eurasia the 
various families of this race wandered westward until they 
occupied all Europe. From Europe, moving still westward, 
they have subjugated the American continent, and even 
now the advance guard is knocking at the doors of Asia, 
after nearly completing the circuit of the world. There 
can be but one explanation of such a wonderful disper- 
sion. It is the struggle for existence — the energy put forth 
to appease the cravings of hunger. 

Man's Relation to Physiography. — The influence of 
man as a geographic agent is often overlooked and the 
far-reaching consequences are seldom appreciated. These 
effects may be classified as interference with the ordinary 
course of natural events, in respect to the surface of the 
land, with respect to climate, with reference to drainage, 
and in the dispersion of life. 

The surface of the land has been modified by man in 
many ways. Of these the most important is the destruc- 
tion of forestry. In both Europe and the United States 



348 PHYSICAL GEOGRAPHY 

a very large part of the surface once forest-clad is now 
bare. By various artifices, running streams have been 
made to cover enormous surfaces with fluviatile deposits, 
and by the same process immense volumes of soil have 
been removed from one place to be transported to another 
and more available locality. 

Piers and sea-walls have been built in such places as to 
extend shores to a considerable distance seaward. Thus, 
nearly one-third the area of the Netherlands has been 
reclaimed from the ocean ; Venice has become a city of 
the mainland; and considerable areas of Chicago, New 
York, Boston, and San Francisco are built upon land that 
has been made by the industries of man. 

The various highways, roads, railways, and canals, to- 
gether with the levelling and filling that accompany the 
growth of cities and towns, form a permanent record of 
mankind. More than this even, is the surface covered by 
the rubbish carted from cities and spread here and there. 
It is estimated that the surface of Jerusalem has been 
buried many feet by the accumulating rubbish. In places, 
the city of Home has been filled forty feet deep, and the 
same result has obtained in the vicinity of other cities. 

By the diversion of drainage, swamps have been changed 
to dry land and their flora entirely replaced by other 
species. By canals and ditches, lakes have been drained 
and the lake basins given up to cultivation. By systems 
of levees and jetties, river-basins have been limited in area, 
and the area of sediment-depositing has been changed from 
one place to another. 

Perhaps the most important changes that have resulted 
from the hand of man, however, are connected with the 
dispersal of life. Through his agency various species 
have been transported to all habitable parts of the earth ; 
many species have become extinct, and the habits of still 



MAN 349 

others have been greatly changed. It requires only a 
brief geological period until the interference of man shall 
prove to be one of the most important of physiographic 
agents. 

QUESTIONS AND EXERCISES.— Why will not the ordinary laws 
concerning the distribution of life apply to the dispersal of man ? 

Make a list, as complete as you can, of the various races and families 
now in the United States ; from what part of the world did each come? 

Name the advantages possessed by man over other species in over- 
coming the restrictions imposed by his environment. In what ways 
can he override such barriers as the sea, deserts, polar regions, and 
regions not habitable by other species ? 

How, and in what instances, has the discovery of gold affected the 
migration and dispersal of man ? 

Mention one or more instances in which this dispersal has been caused 
by an enemy. 

COLLATERAL READING AND REFERENCE. 

Shaler. — Nature and Man in North America. 
Minn.— Realm of Nature, pp. 320-327. 
Marsh. — The Earth as Modified by Human Action. 
Mindeleff. — Migrations of the Cliff Dwellers — Bureau of 
Ethnology. 

Deniker. — Races of Man, pp. 456-466. 



NOTES 

1 Man is the only animal that habitually walks erect — that is, 
with the spinal column perpendicular to the plane of the feet. 

a Healthy lung tissue, or that of the heart, the liver, the muscle 
are so closely alike in structure that a section from one animal 
serves perfectly as an illustration of the corresponding tissue of 
another. 

3 The futility of even the most carefully made classification is 
apparent when one considers the various interbreeding and amal- 
gamation of races. For instance, the Romanic family embraces 
the five peoples enumerated in the foregoing table. But the 



350 PHYSICAL GEOGRAPHY 

Romans were a mixture of Latins, Sabellians, and Etrurians, only 
one element of which is known certainly to be of Aryan descent. 
An infusion of Greek blood developed the righting powers of the 
mixed race, and led to the conquest of the greater part of Europe. 
When the Western Empire had broken into fragments, the Latin 
language was finally modified by the different races who had 
adapted it, to Spanish, French, Portuguese, and Italian. But 
the Spanish were a mixture of Keltic and Iberian blood, the 
French were of Keltic and Gallic stock, and the Portuguese of 
Keltic, Gallic, and Iberian descent. Now a certain amount of 
Roman blood was intermixed with all these peoples, but in 
hardly an instance is there physically a race characteristic among 
them that is distinctively Roman. A similar mixture took place 
in the case of the English people. Although popularly known 
as Anglo-Saxons, the amalgamation is far more extensive ; it in- 
cludes Angles, Saxons, Jutes, and Danes, together with a general 
mixture of Gothic blood. To this must also be added the infu- 
sion of Latin blood that came with the Norman Conquest. 

4 The Caucasians, a people south of the Caucasus Mountains, 
who are usually taken as the best type of the white races, belong 
to this family. 

6 Among the various races of Madagascar the Hovas are fore- 
most, and in respect to intellectual development are not surpassed 
by any other African peoples. 

6 In spite of the free use of red pigments which the Indians 
were accustomed to use on their faces, a prevailing characteristic 
of the race is the color of the skin, which inclines to a copper- 
red. This feature is not true of the Pacific-coast Indians, how- 
ever, all of whom are distinguished by swarthy or black-brown 
skins. The term ' ' red men ' ' is one that has been not wisely 
chosen. 

7 Among the pre-historic peoples of the continent none have 
excited more interest than the mound-builders and the cliff- 
dwellers. According to popular belief both were a distinct race 
of people whom the Indians exterminated. As a matter of fact, 
they were nothing more nor less than Indians. At the time of 
the discovery of America by Columbus, some of the native Amer- 
icans, the Aztecs for instance, were in early stages of civilization. 
Most of them, however, were still in the stone age, and were 
therefore in a state not higher than barbarism. Still others 



MAN 351 

were in an intermediate state, and these had begun to forsake 
the wickiup or tepe for houses constructed upon architectural 
principles. The tribes who had reached this development were 
responsible for mound-building - . The Seneeas, Mohawks, and 
Iroquois had begun to build the famous long houses ; the Shaw- 
nees, Cherokees, and Delawares had not reached quite so high a 
plane, and were still mound-builders. The cliff-dwellers were 
emerging from barbarism and built their pueblos of selected 
stone. For better protection they commonly built them on high 
mesas, on cliff-terraces, or even in caves. The Aztecs, to whom 
the Zunis and Moquis are the nearest living approach, were on a 
much higher plane and seem to have emerged from barbarism 
at the time of the conquest of Mexico. 

* Some of the Abyssinians are certainly Semitic, but for the 
greater part these are comprised in the nomadic Arabs who have 
gradually extended their limits to a large part of Africa. The 
earlier inhabitants are Aryans, however. 

9 The existence of pygmy tribes is mentioned by Herodotus, 
Pomponius Mela, Aristotle and others, but as recently as thirty 
years ago it was believed that the accounts of them were mythical. 
In 1865 the famous African traveller, Paul Du Chaillu, dis- 
covered the Obongo tribe, being the first one in modern times to 
do so. His accounts were flatly contradicted in Europe, but a 
few years later they were confirmed by Pere des Avanchers, an 
Abyssinian missionary. In 1871, another tribe, the Akka, were 
discovered by Dr. Schweinfurth. 

'" It is by no means certain that man did not precede the 
Glacial epoch. A skull found by Professor Whitney among 
Pliocene deposits and various other relics found among the 
auriferous gravels of California, indicate a much greater age than 
post-glacial existence. As a matter of fact, the search for pre- 
historic and fossil man has been neither extended nor systematic. 
Practically no investigations have been made among the Miocene 
deposits of Central and Southern Asia, where of all places sys- 
tematic researches should be made. 

11 This piece is now in the British Museum. Of its origin and 
antiquity there is no doubt. 

12 The Tartars overran Russia, Turkey, and Hindustan. They 
are among the most intelligent of the Turanic peoples. 



CHAPTER XX 
THE INDUSTRIAL REGIONS OF THE UNITED STATES 

The main body of the United States extends from the 
colder part of the Temperate Zone to the Torrid Zone, 
the isotherm forming the northern boundary of the latter, 
crossing the southern parts of Florida, Texas, and the 
lower part of the basin of the Colorado River. This part of 
the United States is divided naturally into physiographic 
regions that have fairly well-defined boundaries ; and 
because of their features of surface and climate, each re- 
gion has become a great centre of industries that are pe- 
culiar to it. 

The boundaries of these regions are both topographic 
and climatic, and the regions themselves differ from one 
another in either climate or topography, or in both. 
Roughly speaking, the groups of States commonly recog- 
nized do not differ very greatly from the industrial groups 
that result from diverse conditions of climate and to- 
pography. 

The following are the principal physiographic and in- 
dustrial regions : The New England Plateau, including 
the eastern part of New York ; the Middle Atlantic States, 
including the Atlantic Coast Plain and the middle and 
southern Appalachian Highlands ; the Great Centred Plain, 
including the regions commonly known as the Northern 
States and the Southern States ; the Western Highlands, 
including the region west of the 2,000-foot contour, the 
Rocky Mountains, the Columbia Plateau, the Colorado 

352 



354 



PHYSICAL GEOGRAPHY 



Plateau, the Basin, the Sierra Nevada and Cascade Moun- 
tains; and the Pacific Coast Region. Make a list of these, 
grouping each subdivision under its principal division. 

The New England Plateau. — This region embraces 
the northern Appalachian folds, with here and there areas 
that belong to the Laurentian highlands. During the 
glacial epoch this region was greatly worn. The Appa- 
lachian folds in places were almost obliterated, and the 




THE RUGGED SURFACE AFFORDS WATER-POWER 



Green, White, Adirondack, and Catskill Mountains are 
the principal remnants. Here and there are isolated 
" monadnocks," most of which are bosses of volcanic rock 
which were able to withstand the erosion and corrosion 
that resulted from the work of the ice age. Granitic rocks 
prevail, and their rounded surfaces are generally smooth 
and polished. 

As a result of the glacial epoch the surface of the New 
England Plateau is very rugged, the only level regions 



INDUSTRIAL REGIONS OF UNITED STATES 355 

being the river flood plains and the old lake basins whose 
waters have disappeared. Many lakes still remain, how- 
ever, and these, a few coast lagoons excepted, have very 
strongly the character of glacial lakes and tarns. Name 
six of the largest. The slope is somewhat abrupt and, as 
a result, the rivers flow in " reaches " ; that is, stretches of 
slack water alternate with rapids and falls. 

The coast region is equally peculiar, and, inasmuch as it 
has been submerged or "drowned "in comparatively re- 




A HARBOR COAST 



cent geological times, the sea now intrudes upon the gla- 
ciated regions, making the whole shore-line one of fjords, 
like those of Norway. Practically all the good harbors 
of the Atlantic coast of the United States are confined to 
this region and, as a result, about four-fifths of the foreign 
commerce of the country goes in and out of its ports. 



356 PHYSICAL GEOGRAPHY 

The rugged surface may be classified as uplands and 
valle}^ lands. The uplands are characterized by thin and 
innutritious soil. The surface is diversified by drumlins, 
eskers, and granite hog backs ; and much of it is strewn 
with erratic bowlders. The uplands are not capable of 
supporting a dense population, 1 and in the past half cen- 
tury there has been no material progress in agricultural 
pursuits ; on the contrary, farming lands have depreciated 
in value. About all the industrial gains have been associ- 
ated with manufacture. How does the surface affect this 
industry ? The farming is confined to the lowland valleys 
and restricted to garden and dairy products. This region 
is celebrated for the manufactures that require a high 
degree of intellectual and mechanical skill, 2 and these 
have resulted from the conditions that have afforded the 
abundant water-power. The manufactures form a large 
proportion of the nation's foreign exports. The sewing- 
machines, bicycles, clocks, and firearms made in the mills 
and factories of this region are shipped to almost every 
part of the world ; the cotton cloth is used by about every 
race of people. 

The Middle Atlantic States. — This region includes 
the principal part of the Atlantic Coast Plain, together 
with the middle and southern Appalachians. The lower 
part of the Coast Plain consists of a belt of swamp lands 
bordered by sandy pine-barrens. Beyond these there is a 
belt of Piedmont lands — the foot-hills of the Appalachian 
Mountains. The rivers flow into estuaries that reach usu- 
ally to the foot-hills and are generally navigable to this 
line — the " Fall Line." From any good map make a list of 
cities along the Fall Line. 

The soil of this region is not well adapted either to cot- 
ton or wheat, although small quantities of both are grown. 
The chief crops are early fruit and garden stuffs, and these 



INDUSTRIAL REGIONS OF UNITED STATES 357 

tind a ready market in the great cities of the manufactur- 
ing region. Cotton and tobacco are important crops in 
the southern part of the Piedmont lands ; and on account 
of the water-power, uoav tardily developed, the manu- 
facture of cotton textiles is rapidly becoming the leading 
industry. 3 

A peculiar feature of the coast is noticeable in the wave- 
formed spits or barrier beaches of this region. How do 




COM. GIVES THK POSSIBILITY OF MAKING STF.FI. 



these barrier beaches affect commerce ? Explain how the 
barrier beach, with the enclosed lagoon, finally becomes a 
part of the Coast Plain. The soil of these beaches pro- 
duces a cotton fibre of long staple and great strength, ;in»l 
this is their chief product. The fibre is used in the web 
of bicycle-tires. 



358 



PHYSICAL GEOGKAPHY 



The montane part of this section is low and not very 
rugged in the northern, but much higher in the southern 
part. The Appalachian folds contain the most productive 
coal measures in the world, and for this reason they are 
the seat of extensive iron and steel manufactures. 

In a few instances the iron ore occurs in the vicinity of 
the coal measures, but in most instances cheap transporta- 
tion by water enables the manufacturer to ship the ore to 




THE CHIEF GRAIN FIELD OF THE WORLD 



the coal mines at a minimum of expense. In a few lo- 
calities, the coal shipped by canal meets the iron ore 
brought in steamers and barges from the Lake Superior 
iron mines to the shores of Lakes Erie and Michigan, and 
great steel-making plants have grown up at Chicago, Cleve- 
land, Lorain, Toledo, Ashtabula, and Buffalo. 

From the foregoing it is apparent that the entire Appa- 
lachian region, both folds and plateaus, is an area of manu- 
facture because of certain geographic conditions, and these 



INDUSTRIAL REGIONS OF UNITED STATES 359 

are the existence of power. The waterfall is stored-up 
power and so also is the coal. The power within the coal 
not only makes the steam that drives so much machinery, 
but in the smelting furnace it also separates the iron from 
the ore ; and inasmuch as iron and steel form the basis of 
most manufactures, the existence of coal implies the de- 
velopment of a great centre of manufacture. 4 

The Great Central Plain. — From Hudson Bay to the 
Gulf of Mexico the Great Central Plain is characterized by 
a level or a gently rolling surface, sloping on each side 
toward the Mississippi River — the whole declining gently 
from a slight rise, called the Heights of the Land, to the 
Bay on the north and the Gulf on the south. Trace the 
Heights of the Land on the map, p. 353. Within what 
limit of elevation is the greater part of its surface ? What 
is the general elevation west of the Missouri River ? 

Most of the rivers flow in channels that are from one 
hundred to three hundred feet lower than the general level 
of the land, and their high banks are the bluffs of this re- 
gion. For the greater part of their extent the bluffs are 
not less than one or two miles apart, and there is a very 
level flood plain between them — the famous "bottom 
lands." All through the Great Central Plain the soil is 
naturally veiw fertile ; that of the bottom lands is espe- 
cially productive. 

The level surface and the general conditions of topog- 
raphy make this region one of sameness so far as external 
appearance is concerned. Climatic conditions, however, 
make two separate and distinct areas of history and indus- 
try ; therefore it is divided into Northern States and 
Southern States. The two groups are roughly separated 
by a boundary formerly known as " Mason and Dixon's 
line," and this boundary in former years was sharply de- 
fined. Incidentally it was a boundary between " free 



360 PHYSICAL GEOGRAPHY 

States " and " slave States," but the real boundary was one 
that separated the cotton-growing region from that in 
which food-stuffs and manufactured goods were the staple 
products. 

In the Northern States wheat, corn, oats, and grass have 
always been the chief products. Because of the level 
surface and the deep, nutritious soil the grain crops can 




A MODERN HARVESTER 
It could not be used in a rugged country. 

be both planted and harvested at the minimum of ex- 
pense. Under no other conditions of topography could 
there have been such a wonderful development of plant- 
ing and harvesting machinery. As a result, this region 
has become one of the principal food-producing regions of 
the world. It produces one-fourth of the world's crop of 
wheat, a considerable proportion of the dairy products, 
and about three-fourths of the corn, most of the latter 
being fed to hogs and converted into pork. 



INDUSTKIAL REGIONS OF UNITED STATES 361 

The western part of this region — the part beyond the 
2000-foot contour — does not receive an amount of rain suf- 
ficient to mature grain ; but the bunch grass and the al- 
falfa 5 crops are the food of great herds of cattle. As a 
result, the Northern States of the Great Central Plain 
produce the flour and meat not only for the United States, 
but much of that required by the rest of the world. 

The Southern States produce about four-fifths of the 
world's supply of cotton. Grain can be grown in these 
States but, acre for acre, the crop does not pay nearly so 
well as cotton ; and cotton cannot be grown north of the 
line that separates the two groups. The industries and 
social conditions — and, therefore, the history — of the two 
sections have differed greatly. How did these conditions 
encourage slavery in the one group and discourage it in 
the other ? 

There has always been a considerable amount of man- 
ufacture in both sections, but the manufactured articles 
have been closely related to the grain and the meat prod- 
uct in the one section, and to cotton-growing in the other. 
These manufactures, moreover, have been greatly en- 
couraged by the extensive coal measures mainly in the 
northern section. Most of the cotton is shipped abroad, 
to be made into textiles elsewhere. 

The Western Highlands.— The Western Highlands 
embrace all that region between the eastern foot of the 
Kocky, and the western foot of the Sierra Nevada and 
Cascade Ranges. This region is characterized by rugged- 
ness. The lofty ranges that form the rims of the high- 
land are less than two miles in altitude in few places only. 
Fremont and South Passes are the chief channels of in- 
tercommunication on the eastern side. On the west the 
Central Pacific Railway crosses flic range at an altitude 
of nearly 10,000 feet. In flic north the canons of Columbia 



362 



PHYSICAL GEOGRAPHY 



River and its tributaries afford grades not too difficult for 
railway communication ; on the south the canons of the 
Rio Grande, together with San Gorgonio, and Tehachapi 
Passes — the latter at the southern junction of the Sierra 
Nevada and Coast Ranges — are the chief routes of com- 
merce. 

The ranges of the Rocky Mountains are lofty folds rest- 
ing each on a core of granitic rocks. The Sierra Nevada 




HAGERMANS PASS 
The ranges and canons are a barrier to intercommunication. 

and Cascade Ranges are huge blocks of tilted rock with a 
gentle slope on the west and an abrupt escarpment on the 
east. The parallel ridges of Nevada and Oregon, com- 
monly called the " Basin Ranges," are excellent examples 
of block mountains, the upturned edge of the block con- 



INDUSTRIAL REGIONS OF UNITED STATES 363 

stituting the range. Here and there are the isolated 
knolls that form the laccolites of which the Henry Moun- 
tains are examples. 

The western slopes of the Sierra Nevada and Cascade 
Ranges receive a generous rainfall ; consult the wind 
chart, p. 221, and explain why. Within the rim ranges 
the rainfall is deficient. In the northern part it is suf- 
ficient for a rather scanty pasturage, but the southern part, 
the higher plateaus excepted, is a desert. 

The Columbia Plateau, or " Plains of the Columbia," is 
mainly the surface of the great flood of lava that seems to 
have flowed from several fissures on the Sierra Nevada 
Mountains. 6 The general surface of the plateau, the block 
ranges excepted, is fairly level, but the region has been 
much dissected by the rivers, whose canons are from five 
hundred to more than three thousand feet deep. 

The Colorado Plateaus, sometimes called the " Alcove 
Lands," consist of a series of table-lands varying from half 
a mile to a mile and a half in altitude. The lower plateaus 
are desert regions of tropical temperature, with here and 
there a few tribes of squalid Indians. The middle plateaus 
have sufficient rain for a very scanty covering of grass ; the 
higher mesas have a fair growth of grass and timber. 

Canons with angular outlines and almost vertical walls 
are the chief characteristic of this region. The canons of 
the Colorado, which have made the region famous, in 
places are more than a mile deep. Probably nowhere else 
on the face of the earth are the features of erosion and cor- 
rosion presented on such a stupendous scale. Every mas- 
ter stream and every tributary is practically an underground 
stream, so deep are their channels below the general level 
of the plateaus. 

The Basin Region receives its name from the fact that 
none of its drainage reaches the sea. On the slopes of the 



364 PHYSICAL GEOGRAPHY 

block ranges the rivers are vigorous streams, but their 
waters finally disappear by evaporation and percolation in 
the sea of fine rock waste at their bases. 7 The lakes are 
without outlet to the sea, and most of them are the shrunk- 
en remnants of two great lakes that once covered a large 
part of this region. 

One of these, now called Lake la Hontan, included Hum- 
boldt, Pyramid, Winnemucca, and several other lakes ad- 
jacent. Several of them, including Walker and Owens 
Lakes, have never wholly disappeared and their waters are 
saturated brines, evaporation continuing until the water can 
hold no more saline matter in solution. Great Salt, Utah, 
Sevier, and Parowan Lakes are the remnants of former 
Lake Bonneville (p. 173). Of the various remnants half a 
dozen have wholly disappeared, and Sevier and Parowan 
Lakes are practically dry. Utah Lake is fresh ; why ? 
Great Salt Lake at present is shrinking on account of the 
diversion of its feeders for purposes of irrigation. 8 

Two small areas of the Basin Region are below sea -level. 
One of these, Salton Lake and its basin, are undoubt- 
edly the former head of the Gulf of California ; the other, 
Death Valley, may have been. The " sink " on dry bed of 
Salton Lake, also known as Coahuilla Valley, on the Sink 
of San Felipe, was most likely separated from the present 
Gulf by the sediments brought down by the Colorado 
River. The sediments made a bar or sea-wall across the 
Gulf and cut it in twain. The upper portion in places has 
become partly filled with wind-blown rock waste, but its 
lowest part is about three hundred feet below sea-level. 
Death Valley, at Kings Springs, is nearly two hundred and 
fifty feet below mean tide. 

Several of the sinks of this region are fed, not by rivers 
that normally flow into them, but by the overflows of the 
Colorado River. When more than bank-full, the latter 



INDUSTRIAL REGIONS OF UNITED STATES 365 

overflows into the lower laud to the westward. Former 
Saltoii Lake was an overflow of this character. 9 New and 
Hardy's Rivers, frequently chartered on maps of this re- 
gion, are not streams flowing into the Colorado, but out of 
it. In this locality the river practically flows around the 
side of a slope ; and at times, when its channel is choked 
with sediment, the water breaks its confining bank and 
temporarily flows out into the desert. 




MOUNT RAINIER 
// is the cinder-cone of an extinct volcano. 



The climate of the Basin is one of intense heat, and the 
southern part is tropical. In many places it is a region 
of dunes swept by simoons, and occasionally deluged 
by cloudbursts. To the latter are mainly due the sinks 
and washes of the region. Yuccas, cacti, mezquit (a spe- 
cies of acacia), and gamma, a coarse grass resembling the 
spinifex of Australia, are the prevailing vegetation of the 
southern part; sage-brush, a kind of wormwood, is char- 
acteristic of the northern region. Wherever irrigation is 



366 PHYSICAL GEOGKAPHY 

possible the soil of the river flood plains is highly pro- 
ductive. In the southern part several species of lizard, 
among them the " horned toad," abound. A large species, 
popularly known as the " Gila monster," inhabits the Gila 
River and is peculiar to this river valley. Herds of deer 
are found near the head of the Gulf of Colorado ; and a 
few camels, the descendants of imported animals, 10 are run- 
ning wild along the lower part of the river. 

In general, the conditions of both climate and topogra- 
phy will not permit the Western Highlands to become a 
thickly peopled region. The rainfall is insufficient for 
the production of food-stuffs, and the latter must depend 
upon irrigation wherever they are grown. The rugged 
surface is intensified by the deep and precipitous stream 
canons, and these are such obstacles that commerce is 
carried on only at an enormous expense. In one or two 
instances a canon half a mile in width forces traffic to make 
a detour of several hundred miles around. The mining 
of copper, lead, and the precious metals is the most im- 
portant industry. 

The Pacific Coast Region. — This region includes 
the western foot-hills of the Sierra Nevada and Cascade 
Ranges, the Coast Ranges, and the great intermontane 
valley between them. The principal feature of this re- 
gion is the distribution of rain. During the winter months 
the moist westerly winds are sufficiently chilled to shed an 
abundance of rain over almost the entire region. Scarce- 
ly a drop falls from May to October. The rainfall, there- 
fore, is seasonal. 

The foot-hill region is more or less rugged, but the 
greater part of its area forms excellent ranges for cattle 
in the north, sheep in the south, and fruit in every part. 
The Coast Ranges lie abruptly against the shores of the 
Pacific Ocean and in only a few places is there even 



INDUSTRIAL REGIONS OF UNITED STATES 3G7 



a narrow coast plain. The few harbors, however, are 
deep, commodious, and most conveniently situated. In a 
few places, however, vessels lie alongside a high cliff and 
receive their cargoes by means of chutes with long out- 
riggers. The lower ranges of these mountains form ex- 
cellent pasturage ; the river valleys produce the best 
wheat that is grown. 

The great intermontane valley is probably a marine 
plain. It varies from twenty to about one hundred miles 
in width, but in sev- 
eral places it is in- 
terrupted by cross 
spurs that connect 
the great ranges. 
In the north, where 
it opens to the sea, 
it is known as the 
Sound Valley. 
What strait and 
sound form the out- 
let ? Farther south 
the Golden Gate 
opens from the sea 
into one of the prin- 
cipal harbors of the world ; what is its name ? This part of 
the intermontane region is best known as the Sacramento- 
San Joaquin Valley. 

The northern and southern parts of the intermontane 
valley form a mammoth wheat field; n the middle portion 
consists of rolling lands that form excellent cattle and 
sheep ranges, and furnish the possibilities of unlimited 
water-power not yet utilized. South of Tehachapi Pass a 
fertile lowland lies next the Pacific which yields an abun- 
dance of semi-tropical fruits and a very fine merino wool. 




PATH OF A SNOW SLIDE 



368 PHYSICAL GEOGEAPHY 

The conditions of both climate and topography make this 
a region that is capable of supporting an enormous popu- 
lation. 

The Territory of Alaska forms the northern part of the 
Pacific Coast region. Its climate and rugged surface ren- 
der it unfit for all agricultural pursuits. The coast slope 
is moderately warm, but the rainy season is about ten 
months in duration ; the interior is a region of arctic 
temperature. So far as is known there is not a level tract 
of cultivable land large enough to make a fair-sized farm. 
The chief wealth of the territory is contained in the gold 
mines of the Klondike and Cape Nome Districts and in 
the fisheries of the littoral waters. 

The Adjustment of Industrial Pursuits to Environ- 
ment. — In the growth and development of a nation two 
processes usually are going on — the acquisition of territory 
and the adjustment of the pursuits of a people to the condi- 
tions of their geographic surroundings. The latter is usu- 
ally attended with more or less friction, and the friction 
is a very large factor in their history. 

In the geographic distribution of the industries of the 
United States, one may follow the processes of adjustment. 
The New England Plateau, with its abundant water-power — 
helped also by steam-power — furnishes the country with 
light manufactures and textiles and exports the balance. 
The people of the harbor region carry on the foreign com- 
merce and largely control the great railway systems that 
transport the manufacturer's products and the food-stuffs. 

The people of the Appalachian region manage the distri- 
bution of the coal and supply the country with steel rails, 
bridge material, building girders, and power-producing ma- 
chinery. From the prairies of the Great Central Plain 
come the breadstuffs and meat, and from the Atlantic 
Coast Plain the fruit and vegetables required for the labor- 



City of 
NEW YORK 

and Vicinity, 

■with 
Harbor Approaches 




370 PHYSICAL GEOGRAPHY 

ers in the crowded manufacturing centres. From the youth 
comes the cotton and from the west the wool that is to 
clothe eighty millions of people. From the Western High- 
lands are obtained the gold and silver, the medium of com- 
mercial exchange, and much of the copper the medium by 
which electric-power is transmitted. Each section sup- 
plies not only the rest of the United States, but a large 
foreign trade as well. 

In general, the area which produces the food-stuffs and 
timber means great population. The gold and silver mean 
a vast commerce. The coal and the iron ore are forecasters 
of tremendous power. 

Natural Resources. — No other nation possesses a 
greater wealth of resources than the United States. Some 
of these will still last for years, but others are nearly ex- 
hausted. The bison and the fur-seal are practically extinct, 
the former being in part replaced by cattle that certainly 
are of greater value. 

The most valuable forest trees of the country are the 
pines. Of these, a belt of white pine extends along the 
northern border ; and a belt of yellow pine along the At- 
lantic and Gulf coasts. Both of these regions are nearly 
exhausted of their supply of merchantable timber. 1 ^ The 
dense forests of Douglas fir, or " Oregon pine," and red- 
wood of the Pacific Coast will be productive for a much 
greater length of time. The amount of growing timber is 
probably greater than at any previous time in the history of 
the country, but most of it is not adaptable for building pur- 
poses. It is estimated that from five to ten million young 
pines are destroyed each year for use as Christmas trees. 

The coal-fields cover an area of about 130,000 square 
miles. 13 Of the amount yielded from these mines, all the 
anthracite coal comes from three small areas in Pennsyl- 
vania; these, it is estimated, will be exhausted in about 



INDUSTRIAL REGIONS OF UNITED STATES 371 

one hundred years. The supply of bituminous coal is prac- 
tically unlimited. Much of the coal-supply is used as 
house fuel, but by far the greater part is used in the manu- 
facture of iron and in producing steam. 

Coal is derived from woody fibre that in time past was 
subjected to heat and pressure away from contact with the 
air. Most of the vegetable matter accumulated in the 
swamps of the Carboniferous Age. The coal measures 
of the Pacific Coast, however, are of much more recent 
origin, and formed during the Tertiary period. 

Petroleum, or rock oil, occurs in various places, usually 




A GATEWAY OF COMMERCE 



near but not always in the coal-fields. The refined oil of 
commerce is shipped to almost every part of the world, 
and is even an article of caravan trade in Africa. The 
principal wells of the United States are in Western Penn- 
sylvania, Eastern Ohio, and West Virginia. There is also 
a productive region in Southern California. Natural gas 
occurs in the same general area, but the gas and the oil 
do not seem to be associated. The gas is used for house 
fuel and for making steam. The supply, much of which 
has been wasted, is becoming exhausted. 

Iron ore occurs in very many parts of the United States, 



372 PHYSICAL GEOGKAPHY 

but it is available only when it can be shipped to places 
where coal is cheaply obtained. The Gogebic and Ke- 
weenaw deposits on Lake Superior, Iron Mountain in Mis- 
souri, and the deposits of the Appalachian Mountains are 
the chief supplies. The iron is obtained from the ore by 
smelting the latter with coal or. coke. The "pig-iron" 
resulting is then converted into steel ingots by the Besse- 
mer process, and the ingots are rolled into rails, plates, 
and billets, and other structural material. 

Gold is abundant in the Western Highlands. It is 
obtained mainly by crushing the quartz rock in which it 
occurs and " amalgamating " or dissolving the gold in 
quicksilver, or by the use of other solvents. In Alaska 
and in parts of California most of the gold is free, being 
mingled with gravel. It is obtained by " washing " the 
latter away with water, thereby leaving the gold, which is 
much heavier, to be taken up by the quicksilver. Silver 
also occurs in the Western Highlands. Copper occurs in 
the Rocky Mountains, but the principal part of the prod- 
uct comes from the Lake Superior region. It is mainly 
used for the transmission of electric power. One of the 
two quicksilver-producing regions of the world is in Cali- 
fornia and this state yields about half the output. 



QUESTIONS AND EXERCISES.— Repeat the list of physiographic 
and industrial regions enumerated in the first page of this chapter. 

Why is the New England Plateau ill-adapted to grain-farming ? How 
does topography become a factor in the economic production of grain ? 

State the various ways in which coal is used as power, both on land 
and at sea. 

Study the furniture and equipments of the school-room and make a 
list of the industries there represented. Trace the geographic source 
of the raw material employed ; where is each manufactured ? 

Explain how the topography of the northern prairies has affected the 
development of farming machinery. 

Explain why cotton growing is limited to its present latitude. In 



INDTJSTKIAL EEGIONS OF UNITED STATES 373 

what way has cotton-growing affected the social conditions of the peo- 
ple of the Southern States ? 

Explain how and why the topography of the Western Highlands is a 
barrier to commerce. 

Explain how and why the geographic distribution of industries has 
resulted in the enormous development of railways. 

Describe three railway routes across the Continent ; two water routes 
from Chicago to tide water. 

How does the grade of a railway affect the cost of transporting freight? 

Obtain from the Hydrographic Office, Washington, D. C,any bulletin 
or publication explaining the kinds and uses of buoys and range lights 
employed in harbors. 

Trace the course of a deep draught steamship entering the main 
channel of New York Harbor, with reference to the range lights. {See 
map, p. j6g.) 

COLLATERAL READING AND REFERENCE 

Powell.— Physiography of the United States, pp. 33-100. 

Davis. — Physiography of the United States, pp. 269-304. 

McGrEE. — The Piedmont Plateau, National Geographic Mag- 
azine, vii., 261. 

Hewes. — Statistical Railway Studies, American Railways, 
pp. 425-449. 

NOTES 

1 There has been a constant movement of people from the up- 
land farms either to the cities or else to the more fertile regions 
of the west. 

3 In manufacturing and commercial regions there is a greater 
amount per capita paid for education and higher average daily 
wages than in any other part of the country. 

3 By manufacturing the cotton in the region where it is grown 
there is saved the transportation of the cotton from the field to 
the mills, many miles distant. 

4 The United States now leads in the manufacture of rails. 
Nearly all of the 6,000 miles of steel rails that span Siberia were 
made in the rolling mills of Pennsylvania. 

6 Alfalfa is a hardy and rapidly growing species, very closely 
related to clover. It is fully as nutritious as clover and grows 
more rapidly. 



374 PHYSICAL GEOGKAPHY 

• In several places the Columbia River has cut its channel deep 
into the flood of lava. In one place there is disclosed a forest 
which was overwhelmed by the lava. The trees are felled, but 
the wood is in a good state of preservation. 

7 At times the beds of some of the larger streams, such as Hum- 
boldt and Carson Rivers, are dry in the day but contain a con- 
siderable amount of water at night, when, by reason of lower tem- 
perature, evaporation is lessened. 

8 On the whole there seems to be a slight gain in the volume of 
the lake. Pyramid, Carson, and Winnemucca Lakes, in recent 
times dry, are now filling up. Their waters contain not much 
more than three per cent, of salt. 

9 At the time of the last filling of the basin the water was 
extremely salt, and its temperature was nearly 120° F. Because 
of its altitude — more than three hundred feet lower than the 
Colorado River — at several times there have been propositions to 
turn the river into the sink and thus make an inland sea. 
Evaporation is so great, however, that the entire volume of the 
Colorado would fill but a small part of the basin, nor would 
there be any outflow from the sink to the Gulf. 

10 The camels were first imported by Jefferson Davis, at the 
time when he was Secretary of War. As pack animals they were 
successful. A camel could carry twice as much as the best pack 
mule, and carry it twice as far in a day. The pack mules and 
horses were in mortal terror of the camel, however, and the rifle 
of the packer in time put an end to the experiment — and prac- 
tically to the camel. 

11 The excess of wheat is exported mainly to Europe, by way 
of Cape Horn. The completion of the Nicaragua Canal will 
bring San Francisco nearer to London than its rival wheat mar- 
ket, Calcutta, now is. 

14 Forest fires probably rank first in the destruction of timber. 
The railways make the heaviest demand on the oak, which is em- 
ployed as ties. Between the railways and the tanneries the 
Pennsylvania Appalachians are nearly shorn of oak and hem- 
lock. The paper-makers also use an enormous amount of tim- 
ber in the manufacture of paper pulp. 

13 Only a small portion of this area, however, is productive. 
The coal measures of China probably surpass those of the United 
States. 



APPENDIX 



The Elements of the Solar System 



Name. 


Distance from 
Sun, in Miles." 


Time of 
Revolution. 


Diameter in 
Miles. 


Number of 
Satellites. 


Density 
Water =1 


Sun 






860,000 

2,992 

7,660 

7,918 

4,211 

20—300 

86,000 

70,500 

31,700 2 

34,500 2 




1.4 


Mercury .... 


37,750,000 

66,750,000 

92,300,000 

141,000,000 

250,000,000 

480,000,000 

881,000,000 

1,771,000,000 

2,775,000,000 


88 days 
224 " 
365| " 

1.9 yrs. 

4.4 1 » 
11.8 " 
29.5 " 
84 " 
164 " 




6.8 2 




4.8 2 


Earth 

Mars 


1 
2 


5.6 

4.2 


Jupiter 

Neptune .... 


5 
9 
4 
1 


1.4 
0.7 
1.8» 
1.1 s 



1 The periodic time of the asteroids varies from 3.1 years to 7.8 years ; the approximate 
average is 4.4 years. 

a These values are approximate. 



II 

Deep Borings 

The following are the greatest artificial depths yet obtained, 
that at Monongahela probably extending as far below sea-level 
as any others. The two deepest borings in the world were 
both sunk in Germany, at Government expense, to ascertain 
the thickness of the coal measures, and also whether other 
beds underlay those that were known. The deeper of the 
two and the greatest depth yet attained is in the coal-fields of 
Upper Silesia, at the little mining town of Paruschowitz. where 
the diamond drill has penetrated to the depth of 6,570 feet. 

375 



376 APPENDIX 

The second greatest depth is that at Schladebach, near Leipsic, 
where the drill was sent down to 6,265 feet. With the excep- 
tion of the borings on the Monongahela and Wheeling and 
the deeper of the two wells sunk at St. Louis, all the drilled 
holes that have reached an exceptionally great depth are in 
Germany. Here is a list of the deepest bore-holes : 

Feet. 

Paruschowitz, Upper Silesia 6,570 

Schladebach, near Leipsic ■. . 6,265 

Monongahela (thus far sunk). 5,532 

Wheeling, W. Va 4,920 

Sperenberg (gypsum beds near Berlin) 4,559 

Lieth, near Altona 4,388 

Eu, near Stassfurt 4,241 

Lubtheen, in Mecklenburg 3,949 

St. Louis, Mo 3,843 

Stennewitz, near Halle 3,644 

Inowrazlaw, Posen , . 3,624 

Friedrichsaue, near Aschersleben 3,542 

Many thousands of wells have been sunk in this country 
chiefly in the search for petroleum or natural gas, but most of 
them are not over 1,000 to 2,000 feet deep. The greater part 
of the artesian wells in the country vary from 200 to 1,000 
feet. The average depth of the many thousands of artesian 
wells sunk for irrigation in the western half of the country is 
not far from 210 feet. 

It is in our copper-mining shafts on Lake Superior that we 
take first rank in this form of excavation. Work on No. 
5 Tamarack shaft on Houghton Peninsula began in 1895, and 
it will not be completed until 1901, when, it is expected, it 
will be the deepest shaft in the world. It will not be sunk 
to a greater depth, for from this level the company can ob- 
tain all the ore at that end of its property. There is but little 
uniformity, however, in the rate at which the heat increases ; 
it varies from one degree (F.) in fifty to one in every seventy 
or eighty feet of descent. In some cases the heat is due in 
part to chemical changes in the rock, — C. C. Adams, in Tlie 
New York Sun. 



APPENDIX 



377 



III 
Heights of Plateaus, Ranges, and Peaks 



Plateaus 



Feet. 



Abyssinian 6,500— 7,500 

Allegheny 1,000— 1,500 

Australian 4,500—5,500 

Bolivian 12,000—14,000 

Brazilian 2,800— 2,500 

Colorado 4,500— 6,000 

Columbia 4,000— 5,000 

Dekkan 2,000—2,500 

Guiana 2,000— 3,000 



Heights of the Land, 

Iberian , 

Iran , 

Mexican 

Mongolian , 

New England 

The "Plains," 

The Pamirs 

Tibet 



Feet. 
1,000— 1,500 
2,000— 2,500 
5,000— 6,000 
7,000— 8,000 
3,000— 4,000 
1,000— 1,200 
5,000— 6,000 
10,000—14,000 
15,000—17,000 



Ranges 



Feet. 



Alps 7,000— 9,000 

Altai 6,000—7,000 

Andes 12,000—15,000 

Apennines 3,500— 4,000 

Appalachian 1,500 — 2,500 

Atlas 8,000—10,000 

Balkan 4,000— 5,000 

Blue (Oregon) 4,000— 4,500 

Carpathian 4,500— 6,000 

Cascade 7,500—10,000 

Caucasus 9,000—11,000 

Coast (California) . 2,500— 3,500 



Feet. 



Coast (Canada) 4,500— 8,000 

Dragon (So. Africa). 4,000— 5,000 

Himalaya 16,000—19,000 

Hindu Rush 16,000—18,000 

Jura 2,500—3,500 

Karakorum 18,000—19,000 

Ozark 1,200— 1,500 

Pyrenees 7,500— 9,000 

Rocky (U. S.) 6,000— 7,000 

" (Canada) 9,000—10,000 

Tian Shan ...17,000— 18,000 

Ural 2,000— 4,000 



Peaks 



Feet. 

Aconcagua 23,900' 

Ararat 17,260 

Blanc 15,744* 

Ben Nevis 4,368 3 

Chimborazo (volcano) 20,500 

Cotopaxi (volcano) 16,300 

Dapsang 28,300 

Demavend (volcano) 18,800 

Etna (volcano) 10,875° 

Elbruz 18,526+ 

Everest 29,000'' 

Fremont Peak 13,790 



Feet. 



Fujiyama (volcano) . .14,177 

Hekla (volcano) 5, 100 

Hood 11,900 

Kenia 18,000 

Kilinia Njaro 20,000" 

Kilauea (volcano) Hawaiian 

Islands 4,000 

Logan 19,500 

Marcy, New York 5,467" 

McKinley, Alaska 20,464' 

Mauna Kea (volcano), Ha- 
waiian Islands 1 4,000 



1 Highest in South America. 6 Possibly highest in the world. 

1 Highest in Europe. • Highest in Adiroudacks. 

* Highest in British Isles. ' Probably highest in North America. 

4 Highest in Caucasus. » Possibly highest in Africa. 

• Varies with each eruption. 



378 



APPENDIX 



Peaks {Continued) 



Feet. 

Mauna Loa (volcano) 13,600 

Mitchell, North Carolina... 6,711* 
Hooker, British Columbia.. 15, 700 

Orizaba (volcano) 18,300' 2 

Pike's Peak 14,147 

Popocatepetl (volcano) .... 17,800 

Rainier (Tacoma) 14,441 

St. Elias 18,024 

1 Highest in Appalachian System. 

2 Highest in Mexico. 

' Possibly highest in world ; not surveyed. 



Feet. 



Shasta 14,440 

Sinai 8,600 

T. 45 (Himalayas) 29,100 3 

Teneriffe 12,000 

Washington 6,286 4 

Vesuvius (volcano) 4,000 5 

Whitney 14,898 6 

Wrangell 17,500 

4 Highest in White Mountains. 
6 Highest in Sierra Nevada Range. 
* Varies with each eruption. 



IV 

Lengths of Eivers and Areas of their Basins 1 



Miles. 

Amazon 4,000 

Amur 2,500 

Brahmaputra 2,000 

Colorado 1,100 

Columbia 1,400 

Danube 1,800 

Dnieper 1,230 

Dwina 700 

Elbe 550 

Ganges 1,800 

Hoang 2,800 

Hudson 300 

Indus.... 2,000 

Irawaddi .1,200 

Kongo 3,000 

La Plata 2,300 

Lena 2,800 

Mackenzie 2,400 

Mekong 2,600 

Mississippi-Missouri. 4,200 



Sq. Miles. 
2,500.000 
750,000 
400,000 
230,000 
290,000 
300,000 
200,000 
150,000 
450,000 
450,000 
400,000 
13,000 
350,000 



1,500,000 

1,250,000 

750,000 

600,000 

300,000 

1,250,000 



Miles. 
Murray -Darling. . 1, 100 

Niger 3,000 

Nile 4,000 

Ob 2,800 

Orange 1,200 

Orinoco 1,500 

Po 450 

Rhine 800 

Rhone 550 

Rio Grande 1,800 

St. Lawrence 2,100 

Sao Francisco. . .1,800 

Seine. 500 

Thames 215 

Tocantins- 1,000 

Volga 2,300 

Yangtze 3,100 

Yenesei 3,000 

Yukon 2,200 

Zambesi 1,800 



Sq. Miles. 

350,000 

1,000,000 

1,250.000 

1,000,000 

275,000 

400,000 

27,000 

90,000 

35,000 

200,000 

560,000 

200,000 

23,000 

6,000 

250,000 

600,000 

700,000 

1,500,000 

400,000 

500,000 



1 Both the length and the area of the basin are approximate except in a few instances ; 
the length of almost every river changes from year to year. 
a Not a tributary of the Amazon. 

It is well to bear in mind that the length of a river is apt to 
vary from year to year, partly because of the formation of 
loops and cut-offs, and partly owing to the gradual extension 
of its headwater tributaries. 



APPENDIX 

V 

Lakes 




379 


Name. 


Area. 


Depth. 


Altitude. 




Square Miles. 

25,000' 2 

1,000' 

13,200 

8,500 2 

170,000 2 

10,0002 

1,300 


Feet. 

200 2 

200 

4,500 

1352 

3,000 2 

20 2 


Feet. 
50 




— 580 




1,400 


Balkash 


1,000' 




-84 


Chad 


1,000 




7,000 




2,300 
700 2 
210 
50 2 
734 
730 






320 

573 

2,300 2 

23,800 

7,000 

22,450 

2,800 


— 1,300 


Erie 


9,960 


Great Salt 


4,200 


Huron 


581 




55 




581 




320 


108 




-267 




31,200 
14,000' 
12,500 
26,000' 
9,400 


1,008 

1,200 

900 


602 




2,670 




12,500 




4,000 




72 


710 







J Approximate ; the figures given are from the best authorities, but vary from the 
measurements of others. Lake Assal is situated in a depression near the Gulf of Aden. 
It is the head of a small bay severed from the sea by aeohan sands. It is fed by a small 
stream that flows from the sea into the lake. The volume of the lake represents the 
balance between inflow and evaporation. , 

2 Subject to great variations ; the sign — prefixed to the altitude indicates below sea 
level. Salton Lake is now dry. 



VI 

The Tides 
The following very clear solution of a much disputed prob- 
lem is given by Dr. Emerson E. White, author of a series of 
mathematical text-books. It is only proper to add that no 
theory on the subject fully explains all the phenomena noted. 
Dr. "White's solution meets the views of most students. 

Let E equal the attraction of the earth, and M equal the attraction of 
the moon at B, and M the attraction of the moon at A and C. 



380 



APPENDIX 



Since distance OB is less than OA or OC, M >M'. Hence E—M<E—M', 
and hence the water at B is lighter than at A or C — i.e., has less specific 
gravity, and is lifted or bulged by the surrounding heavier water. 

Let E equal attraction of the earth and to. equal attraction of moon at 
B', and m' equal attraction of moon at A' or C. Since distance OB' is 




Bit— 



greater than OA' or OC, to < to'. Hence E + to < E + to', and hence 
the water at B' is lighter or has less specific gravity than at A' or C" and is 
lifted or bulged by the surrounding heavier water. Since distance OB is 
less than OB', M > m, and hence the tide at B is higher than at B'. 



VII 

Table Showing the Number of Grains of Moisture, 
by Weight Necessary to Saturate a Cubic Foot 
of Air at Normal Density. 



Temperature. 


Moisture in 
One Cubic 
Foot of Air. 


Temperature. 


Moisture in 
One Cubic 
Foot of Air. 


Temperature. 


Moisture in 

One Cubic 

Foot of Air. 


Degrees F. 
-40 


Grains. 
.08 


Degrees F. 
45 


Grains. 
3.42 


Degrees F. 
68 


Grains. 

7.48 


-30 


.13 


50 


4.08 


70 


7.98 


-20 


.22 


52 


4.37 


72 


8.51 


-10 


.36 


54 


4.69 


74 


9.07 





.56 


56 


5.02 


76 


9.66 


10 


.87 


58 


5.37 


78 


10.28 


20 


1.32 


60 


5.75 


80 


10.94 


30 


1.96 


62 


6.14 


90 


14.79 


35 


2.37 


64 


6.56 


100 


19.92 


40 


2.85 


66 


7.01 


110 


26.43 



INDEX 



Ages, geological, 33 

Altitude, climatic effects of, 242 

Animals, distribution of, 223 

regions of, 316 
Anticyclones, 249 
Artesian wells, 135 
Atmosphere, 21 

movements of, 216 
Asteroids, 17 
Atolls, coral, 47 
Aurora borealis, 272 
Avalanches, 150, 162, 163 
Axis, effects of inclination of, 14, 19 

Balance, Nature's, 23 

Barriers, 310 

Basalt, 27 

Blizzards, 255 

Bores, tidal, 200 

Breezes, day and night, 219 

Brush discharge, 272 

Camel, 39 

in America, 333 
Caverns, 142 
Climate, changes in, 290 

extremes of, 292 

zones of, 291 
Cloudbursts, 246 
Clouds, 234 

cirrus, 236 

cumulus, 236 

nimbus, 237 

stratus, 236 
Coal-fields of U. S., 370 
Coal measures, 39 
Coast forms, 51, 53 
Cold waves, 254 
Comet, Tempers, 18 



Compass, mariner's, 276, 286 

Continents, 42 

Coral formations, 52, 54 

Coronas, 279 

Corrasion, 105 

Craters, 91 

Currents, ocean, 200 

economy of, 205 
Cyclones, 249 

tropical, 250 

winter, 252 

Degradation, 105 
Deltas, 115 
Deserts, 296 

distribution of, 297 

winds of, 223 
Development, stages of, 303 
Dew, 233 
Diffraction, 278 
Divides, migration of, 121 
Doldrums, 219 
Drift, 159, 200 
Drumlin, 159 

Earth, curvature of, 19 

dimensions of, 13 

form of, 12 

motions of, 13 
Earthquakes, cause of, 98 

distribution, 99 

nature of, 95 

phenomena of, 98 
Ecliptic, plane of, 14 
Electricity, laws of, 268, 282 
Environment, 307 

adjustment to, 368 
Equinoxes, precession of, 14 
Eras, geological, 32 



381 



382 



INDEX 



Bros, 17 

Erosion, 105 

Erratic bowlders, 161 

Eruptions, volcanic, 81 

Eskers, 160 

Eskimos, 340 

Estuaries, 115 

Evaporation, latent heat of, 233 

Felspar, 26 

Floes, 193 

Flood-plains, 113 

Forestry, distribution of, 322 

Geoid, 12 
Geysers, 136 
Glacial epoch, 35 
Glacial ice sheets, 155 
Glaciers, 153 

occurrence of, 157 

physiographic effects of, 157 
Grain, 318 
Granite, 38 

Hail, 243 
Halos, 279 

Highlands, western, 361 
Hornblende, 26 
Hydrosphere, 21 

Icebergs, effect of, on commerce, 161 

formation of, 156 
Ice of the sea, 193 
Ice-pack, 173 
Iron, 372 
Islands, 47 
Isobars, 260 
Isoclinal s, 275 
Isogonics, 275 
Isotherms, 291 

Lagoon, 167 

Lakes, accidental, 167 

geographical distribution of, 174 

glacial, 165 

marsh, 164 

physiographic aspect of, 1 69 

playa, 169 



Lakes, salt, 168 

walled, 185 
Land storms, 252 
Life, dispersal of, 309 

nature of, 303 

physiographical aspect of, 327 
Lightning, 283 
Lithosphere, 20 
Lode, 142 
Loess, 227 

Magnetic pole, 274 

storms, 276 

variation, 274, 285 
Magnetism, 273 

laws of, 273 
Man, antiquity of, 342 

migrations of, 345 

races of, 335 
Marshes, 176 

physiographic aspect of, 182 
Matter, forms of, 18 
Mediterraneans, 50 
Meteors, 18 
Mica, 27 
Mirages, 279 
Monsoons, 218 
Moraines, 154 

Mountain-ranges, nature of, 67 
Mountains, distribution of, 70 

economic aspect of, 72 

physiographic aspect of, 69 
Movements of rock envelope, 23 
Mud volcanoes, 138 

Natural resources of U. S., 370 
Neve, 153 
North star, 14* 

Oases, 297 

Ocean waters, physiographic aspect 
of, 206 

Pacific Coast Region, 366 
Passes, 79 
Peat, 177 

Percolating waters, 133 
Physiography, man's relation to, 347 
of under-ground waters, 141 



INDEX 



383 



Plains, distribution of, GO-76 

economic value of, 61 

physiographic aspect of, 01 
Plants, distribution of, 315 

economic, 318 

regions of, 316 

textiles, 322 
Plateau, New England, 354 
Plateaus, distribution of, 64, 78 

economic aspect of, 64 
Potential, electric, 269, 282 
Pygmies, 333, 341 

Rainbows, 280 

Rainfall, distribution of, 238 
seasonal, 240 

Rainless regions, 242 

Rapids, 119 

Rivers, continental, 125 

economic importance of, 120 
geographical distribution of, 123 
growth and development of, 110 
physiography of, 107 

Rock envelope, 21 
formation of, 25 
waste, movement of, 1S3 

Rocks, igneous, 27 
metam orphic. 30 
sedimentary, 27 

Sahara, 301 
St. Elmo's fire, 272 
Sandstone, 28 
Sand valleys, 134 
Sandy hooks, 207 
Sea, 48 

arms of, 49 
Seas, sargasso, 202 
Silica. 26 
Simoon, 223 
Sinter, 141 
Slate, 28 
Sludge, 193 
Snow, 243 



Solar system, 9 
Sphagnum, 177 
Springs, 135 

mineral, 136 
Stalactites, 145 
Stalagmites, 145 
States, Middle Atlantic, 356 
Strata, order of, 30 
Sun and planets, 1 1 
Swamps, 176 

economic value of, 183 

lacustrine, 178 

Talus, 78 

Temperature, extremes of, 294 

mean annual, 300 
Terraces, 115 
Thunder-storms, 271 
Tides, 195 
Tornadoes, 255 
Typhoons, 250 

Underground streams, 139 
Unusual adjustments, 122 

Valleys, 71 
Variation, 305 
Vesuvius, eruption of, 91 
Volcanoes, nature of, 85 

distribution of, 89 
Vulcanism, results of, 86 

Water, 54 

envelope, 22 
Watershed, 127 
Waterspouts, 258 
Waves, 194 

Weather forecasting, 259 
Wheat, 319 
White squall, 57 
Winds, 216 

physiographic effects of, 224 

Zone of fracture, 54 



JUN 29 1900 



